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* s390x: Capture grep output in static PIE checkFlorian Weimer2024-06-202-7/+7
| | | | | | | | | | | The test is not a run-time check, so update the description. Also use readelf -W for a more stable output format and fix an LC_ALL typo. This avoids garbled configure messages: checking for s390-specific static PIE requirements (runtime check)... 0x0000000000000017 (JMPREL) 0x280 yes
* s390x: Regenerate ULPs.Stefan Liebler2024-06-191-0/+60
| | | | | | | | Needed due to: - "Implement C23 log10p1" commit ID 55eb99e9a9d840ba452b128be14d6529c2dde039 - "Implement C23 exp2m1, exp10m1" commit ID 7ec903e028271d029818378fd60ddaf6b76b89ac
* elf: Remove HWCAP_IMPORTANTStefan Liebler2024-06-181-5/+0
| | | | | | | Remove the definitions of HWCAP_IMPORTANT after removal of LD_HWCAP_MASK / tunable glibc.cpu.hwcap_mask. There HWCAP_IMPORTANT was used as default value. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
* elf: Remove _DL_PLATFORMS_COUNTStefan Liebler2024-06-181-2/+0
| | | | | | | | | Remove the definitions of _DL_PLATFORMS_COUNT as those are not used anymore after removal in elf/dl-cache.c:search_cache(). Note: On x86, we can also get rid of the definitions HWCAP_PLATFORMS_START and HWCAP_PLATFORMS_COUNT. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
* elf: Remove _DL_FIRST_PLATFORMStefan Liebler2024-06-181-3/+0
| | | | | | | | | | Remove the definitions of _DL_FIRST_PLATFORM as those were only used in the _DL_HWCAP_PLATFORM definitions and in _dl_string_platform(). Both were removed. Note: Removed on every architecture despite of powerpc, where _dl_string_platform() is still used. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
* elf: Remove _DL_HWCAP_PLATFORMStefan Liebler2024-06-181-3/+0
| | | | | | Remove the definitions of _DL_HWCAP_PLATFORM as those are not used anymore after removal in elf/dl-cache.c:search_cache(). Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
* elf: Remove platform strings in dl-procinfo.cStefan Liebler2024-06-182-7/+0
| | | | | | Remove the platform strings in dl-procinfo.c where also the implementation of _dl_string_platform() was removed. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
* elf: Remove _dl_string_platformStefan Liebler2024-06-181-15/+0
| | | | | | | | | Despite of powerpc where the returned integer is stored in tcb, and the diagnostics output, there is no user anymore. Thus this patch removes the diagnostics output and _dl_string_platform for all other platforms. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
* Convert to autoconf 2.72 (vanilla release, no distribution patches)Andreas K. Hüttel2024-06-172-46/+64
| | | | | | | As discussed at the patch review meeting Signed-off-by: Andreas K. Hüttel <dilfridge@gentoo.org> Reviewed-by: Simon Chopin <simon.chopin@canonical.com>
* Implement C23 logp1Joseph Myers2024-06-171-0/+20
| | | | | | | | | | | | | | | | | | | | | | | | | | | C23 adds various <math.h> function families originally defined in TS 18661-4. Add the logp1 functions (aliases for log1p functions - the name is intended to be more consistent with the new log2p1 and log10p1, where clearly it would have been very confusing to name those functions log21p and log101p). As aliases rather than new functions, the content of this patch is somewhat different from those actually adding new functions. Tests are shared with log1p, so this patch *does* mechanically update all affected libm-test-ulps files to expect the same errors for both functions. The vector versions of log1p on aarch64 and x86_64 are *not* updated to have logp1 aliases (and thus there are no corresponding header, tests, abilist or ulps changes for vector functions either). It would be reasonable for such vector aliases and corresponding changes to other files to be made separately. For now, the log1p tests instead avoid testing logp1 in the vector case (a Makefile change is needed to avoid problems with grep, used in generating the .c files for vector function tests, matching more than one ALL_RM_TEST line in a file testing multiple functions with the same inputs, when it assumes that the .inc file only has a single such line). Tested for x86_64 and x86, and with build-many-glibcs.py.
* s390x: Regenerate ULPs.Stefan Liebler2024-05-241-0/+20
| | | | | | Needed due to: "Implement C23 log2p1" commit ID 79c52daf4740b00bef43e4f5a4281b3480459b38
* s390: Improve static-pie configure testsAdhemerval Zanella2024-02-282-231/+40
| | | | | | | | | | | | | | | | | | | | Instead of tying based on the linker name and version, check for the required support: * whether it does not generate dynamic TLS relocations in PIE (binutils PR ld/22263); * if it accepts --no-dynamic-linker (by using -static-pie); * and if it adds a DT_JMPREL pointing to .rela.iplt with static pie. The patch also trims the comments, for binutils one of the tests should already cover it. The kernel ones are not clear which version should have the backport, nor it is something that glibc can do much about it. Finally, the glibc is somewhat confusing, since it refers to commits not related to s390x. Checked with a build for s390x-linux-gnu. Reviewed-by: Stefan Liebler <stli@linux.ibm.com>
* string: Use builtins for ffs and ffsllAdhemerval Zanella Netto2024-02-011-69/+0
| | | | | | | It allows to remove a lot of arch-specific implementations. Checked on x86_64, aarch64, powerpc64. Reviewed-by: Carlos O'Donell <carlos@redhat.com>
* Refer to C23 in place of C2X in glibcJoseph Myers2024-02-011-1/+1
| | | | | | | | | | | | | | | WG14 decided to use the name C23 as the informal name of the next revision of the C standard (notwithstanding the publication date in 2024). Update references to C2X in glibc to use the C23 name. This is intended to update everything *except* where it involves renaming files (the changes involving renaming tests are intended to be done separately). In the case of the _ISOC2X_SOURCE feature test macro - the only user-visible interface involved - support for that macro is kept for backwards compatibility, while adding _ISOC23_SOURCE. Tested for x86_64.
* S390: Fix building with --disable-mutli-arch [BZ #31196]Stefan Liebler2024-01-302-2/+6
| | | | | | | | | | | | | | | | | | | | | | Starting with commits - 7ea510127e2067efa07865158ac92c330c379950 string: Add libc_hidden_proto for strchrnul - 22999b2f0fb62eed1af4095d062bd1272d6afeb1 string: Add libc_hidden_proto for memrchr building glibc on s390x with --disable-multi-arch fails if only the C-variant of strchrnul / memrchr is used. This is the case if gcc uses -march < z13. The build fails with: ../sysdeps/s390/strchrnul-c.c:28:49: error: ‘__strchrnul_c’ undeclared here (not in a function); did you mean ‘__strchrnul’? 28 | __hidden_ver1 (__strchrnul_c, __GI___strchrnul, __strchrnul_c); With --disable-multi-arch, __strchrnul_c is not available as string/strchrnul.c is just included without defining STRCHRNUL and thus we also don't have to create the internal hidden symbol. Tested-by: Andreas K. Hüttel <dilfridge@gentoo.org>
* Update copyright dates with scripts/update-copyrightsPaul Eggert2024-01-01306-306/+306
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* elf: Do not duplicate the GLIBC_TUNABLES stringAdhemerval Zanella2023-12-191-106/+59
| | | | | | | | | | | | | | | | | | | | | The tunable parsing duplicates the tunable environment variable so it null-terminates each one since it simplifies the later parsing. It has the drawback of adding another point of failure (__minimal_malloc failing), and the memory copy requires tuning the compiler to avoid mem operations calls. The parsing now tracks the tunable start and its size. The dl-tunable-parse.h adds helper functions to help parsing, like a strcmp that also checks for size and an iterator for suboptions that are comma-separated (used on hwcap parsing by x86, powerpc, and s390x). Since the environment variable is allocated on the stack by the kernel, it is safe to keep the references to the suboptions for later parsing of string tunables (as done by set_hwcaps by multiple architectures). Checked on x86_64-linux-gnu, powerpc64le-linux-gnu, and aarch64-linux-gnu. Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
* Avoid padding in _init and _fini. [BZ #31042]Stefan Liebler2023-11-302-3/+1
| | | | | | | | | | | | | | | | | | | | | The linker just concatenates the .init and .fini sections which results in the complete _init and _fini functions. If needed the linker adds padding bytes due to an alignment. GNU ld is adding NOPs, which is fine. But e.g. mold is adding traps which results in broken _init and _fini functions. Thus this patch removes the alignment in .init and .fini sections in crtn.S files. We keep the 4 byte function alignment in crti.S files. As the assembler now also outputs the start of _init and _fini functions as multiples of 4 byte, it perhaps has to fill it. Although GNU as is using NOPs here, to be sure, we just keep the alignment with 0x07 (=NOPs) at the end of crti.S. In order to avoid an obvious NOP slide in _fini, this patch also uses an lg instead of lgr instruction. Then the emitted instructions needs a multiple of 4 bytes.
* elf: Remove LD_PROFILE for static binariesAdhemerval Zanella2023-11-214-8/+12
| | | | | | | | | | | The _dl_non_dynamic_init does not parse LD_PROFILE, which does not enable profile for dlopen objects. Since dlopen is deprecated for static objects, it is better to remove the support. It also allows to trim down libc.a of profile support. Checked on x86_64-linux-gnu. Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
* s390: Use dl-symbol-redir-ifunc.h on cpu-tunablesAdhemerval Zanella2023-11-212-15/+17
| | | | | | | | | Using the memcmp symbol directly allows the compile to inline the memcmp calls (especially because _dl_tunable_set_hwcaps uses constants values), generating better code. Checked with tst-tunables on s390x-linux-gnu (qemu system). Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
* s390: Fix undefined behaviour in feenableexcept, fedisableexcept [BZ #30960]Stefan Liebler2023-10-192-2/+4
| | | | | | | | | | | | | | | | | If feenableexcept or fedisableexcept gets excepts=FE_INVALID=0x80 as input, we have a signed left shift: 0x80 << 24 which is not representable as int and thus is undefined behaviour according to C standard. This patch casts excepts as unsigned int before shifting, which is defined. For me, the observed undefined behaviour is that the shift is done with "unsigned"-instructions, which is exactly what we want. Furthermore, I don't get any exception-flags. After the fix, the code is using the same instruction sequence as before.
* s390x: Fix static PIE condition for toolchain bootstrapping.Stefan Liebler2023-08-182-12/+138
| | | | | | | | | | The static PIE configure check uses link tests. When bootstrapping a cross-toolchain, the link tests fail due to missing crt-files / libc.so. As we explicitely want to test an issue in binutils (ld), we now also explicitely check for known linker versions. See also commit 368b7c614b102122b86af3953daea2b30230d0a8 S390: Use compile-only instead of also link-tests in configure.
* configure: Use autoconf 2.71Siddhesh Poyarekar2023-07-172-109/+129
| | | | | | | | | | | | | | Bump autoconf requirement to 2.71 to allow regenerating configure on more recent distributions. autoconf 2.71 has been in Fedora since F36 and is the current version in Debian stable (bookworm). It appears to be current in Gentoo as well. All sysdeps configure and preconfigure scripts have also been regenerated; all changes are trivial transformations that do not affect functionality. Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org> Reviewed-by: Carlos O'Donell <carlos@redhat.com>
* sysdeps/s390: Exclude fortified routines from being built with _FORTIFY_SOURCEFrédéric Bérat2023-07-101-0/+20
| | | | | | | | Depending on build configuration, the [routine]-c.c files may be chosen to provide fortified routines implementation. While [routines].c implementation were automatically excluded, the [routines]-c.c ones were not. This patch fixes that by adding these file to the list to be filtered.
* Fix misspellings in sysdeps/ -- BZ 25337Paul Pluzhnikov2023-05-3025-43/+43
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* S390: Use compile-only instead of also link-tests in configure.Stefan Liebler2023-05-222-177/+109
| | | | | | | | | | | | | | | | | Some of the s390-specific configure checks are using compile and link configure tests. Now use only compile tests as the link tests fails when e.g. bootstrapping a cross-toolchain due to missing crt-files/libc.so. This is achieved by using AC_COMPILE_IFELSE in configure.ac file. This is observable e.g. when using buildroot which builds glibc only once or the build-many-glibcs.py script. Note that the latter one is building glibc twice in the compilers-step (configure-checks fails) and in the glibcs-step (configure-checks succeed). Note, that the s390 specific configure tests for static PIE have to link an executable to test binutils support. Thus we can't fix those tests.
* Remove --enable-tunables configure optionAdhemerval Zanella Netto2023-03-291-10/+4
| | | | | | | | | | | | And make always supported. The configure option was added on glibc 2.25 and some features require it (such as hwcap mask, huge pages support, and lock elisition tuning). It also simplifies the build permutations. Changes from v1: * Remove glibc.rtld.dynamic_sort changes, it is orthogonal and needs more discussion. * Cleanup more code. Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
* S390: Fix _FPU_SETCW/GETCW when compiling with Clang [BZ #30130]Andreas Arnez2023-02-281-2/+2
| | | | | | | | The _FPU_SETCW and _FPU_GETCW macros are defined with inline assemblies. They use the sfpc and efpc instructions, respectively. But both contain a spurious second operand that leads to a compile error with Clang. Removing this operand works both with gcc/gas (since binutils 2.18) as well as with clang/llvm.
* s390x: Regenerate ULPs.Stefan Liebler2023-02-281-0/+1
| | | | | | | | | Needed due to recent commits: - "added pair of inputs for hypotf in binary32" commit ID cf7ffdd8a5f6da55397e10b3860062944312824c - "update auto-libm-test-out-hypot" commit ID 3efbf11fdf15ed991d2c41743921c524a867e145
* s390: Fix build for -march=z13Adhemerval Zanella2023-02-202-0/+2
| | | | | | | | It fixes the build after 7ea510127e2067e and 22999b2f0fb62. Checked with build for s390x-linux-gnu with -march=z13. Reviewed-by: Arjun Shankar <arjun@redhat.com>
* string: Remove string_private.hAdhemerval Zanella2023-02-171-20/+0
| | | | | | Now that _STRING_ARCH_unaligned is not used anymore. Reviewed-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
* iconv: Remove _STRING_ARCH_unaligned usage for get/set macrosAdhemerval Zanella2023-02-173-4/+4
| | | | | | | | | And use a packed structure instead. The compiler generates optimized unaligned code if the architecture supports it. Checked on x86_64-linux-gnu and i686-linux-gnu. Reviewed-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
* Fix ifunc-impl-list.c build for s390Joseph Myers2023-02-171-1/+1
| | | | | | | | | | | | | | | | | | | | | | Builds for s390 recently started failing with: ../sysdeps/s390/multiarch/ifunc-impl-list.c: In function '__libc_ifunc_impl_list': ../sysdeps/s390/multiarch/ifunc-impl-list.c:83:21: error: unused variable 'dl_hwcap' [-Werror=unused-variable] 83 | unsigned long int dl_hwcap = features->hwcap; | ^~~~~~~~ https://sourceware.org/pipermail/libc-testresults/2023q1/010855.html Add __attribute__ ((unused)) as already done for another variable there. Tested with build-many-glibcs.py (compilers and glibcs) for s390x-linux-gnu and s390-linux-gnu. Note: s390x-linux-gnu-O3 started failing with a different error earlier; that problem may still need to be fixed after this fix is in. https://sourceware.org/pipermail/libc-testresults/2023q1/010829.html
* string: Add libc_hidden_proto for memrchrAdhemerval Zanella2023-02-082-3/+9
| | | | | | | Although static linker can optimize it to local call, it follows the internal scheme to provide hidden proto and definitions. Reviewed-by: Carlos Eduardo Seo <carlos.seo@linaro.org>
* string: Add libc_hidden_proto for strchrnulAdhemerval Zanella2023-02-082-4/+8
| | | | | | | Although static linker can optimize it to local call, it follows the internal scheme to provide hidden proto and definitions. Reviewed-by: Carlos Eduardo Seo <carlos.seo@linaro.org>
* S390: Influence hwcaps/stfle via GLIBC_TUNABLES.Stefan Liebler2023-02-0710-41/+411
| | | | | | | | | | | | | | | | | | | | | | | | | | | This patch enables the option to influence hwcaps and stfle bits used by the s390 specific ifunc-resolvers. The currently x86-specific tunable glibc.cpu.hwcaps is also used on s390x to achieve the task. In addition the user can also set a CPU arch-level like z13 instead of single HWCAP and STFLE features. Note that the tunable only handles the features which are really used in the IFUNC-resolvers. All others are ignored as the values are only used inside glibc. Thus we can influence: - HWCAP_S390_VXRS (z13) - HWCAP_S390_VXRS_EXT (z14) - HWCAP_S390_VXRS_EXT2 (z15) - STFLE_MIE3 (z15) The influenced hwcap/stfle-bits are stored in the s390-specific cpu_features struct which also contains reserved fields for future usage. The ifunc-resolvers and users of stfle bits are adjusted to use the information from cpu_features struct. On 31bit, the ELF_MACHINE_IRELATIVE macro is now also defined. Otherwise the new ifunc-resolvers segfaults as they depend on the not yet processed_rtld_global_ro@GLIBC_PRIVATE relocation.
* string: Improve generic strnlen with memchrAdhemerval Zanella2023-02-061-6/+8
| | | | | | | | It also cleanups the multiple inclusion by leaving the ifunc implementation to undef the weak_alias and libc_hidden_def. Co-authored-by: Richard Henderson <richard.henderson@linaro.org> Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>
* string: Improve generic strchrAdhemerval Zanella2023-02-061-5/+6
| | | | | | | | | | | | New algorithm now calls strchrnul. Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc-linux-gnu, and powerpc64-linux-gnu by removing the arch-specific assembly implementation and disabling multi-arch (it covers both LE and BE for 64 and 32 bits). Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>
* string: Improve generic strchrnulAdhemerval Zanella2023-02-061-2/+0
| | | | | | | | | | | | | | | | | New algorithm read the first aligned address and mask off the unwanted bytes (this strategy is similar to arch-specific implementations used on powerpc, sparc, and sh). The loop now read word-aligned address and check using the has_zero_eq function. Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc64-linux-gnu, and powerpc-linux-gnu by removing the arch-specific assembly implementation and disabling multi-arch (it covers both LE and BE for 64 and 32 bits). Co-authored-by: Richard Henderson <richard.henderson@linaro.org> Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>
* string: Improve generic strlenAdhemerval Zanella2023-02-061-4/+6
| | | | | | | | | | | | | | | | | New algorithm read the first aligned address and mask off the unwanted bytes (this strategy is similar to arch-specific implementations used on powerpc, sparc, and sh). The loop now read word-aligned address and check using the has_zero macro. Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc-linux-gnu, and powercp64-linux-gnu by removing the arch-specific assembly implementation and disabling multi-arch (it covers both LE and BE for 64 and 32 bits). Co-authored-by: Richard Henderson <richard.henderson@linaro.org> Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>
* Update copyright dates with scripts/update-copyrightsJoseph Myers2023-01-06303-303/+303
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* elf: Introduce <dl-call_tls_init_tp.h> and call_tls_init_tp (bug 29249)Florian Weimer2022-11-031-1/+1
| | | | | | | | This makes it more likely that the compiler can compute the strlen argument in _startup_fatal at compile time, which is required to avoid a dependency on strlen this early during process startup. Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
* Use PTR_MANGLE and PTR_DEMANGLE unconditionally in C sourcesFlorian Weimer2022-10-183-2/+10
| | | | | | | | | | | | | | | | | In the future, this will result in a compilation failure if the macros are unexpectedly undefined (due to header inclusion ordering or header inclusion missing altogether). Assembler sources are more difficult to convert. In many cases, they are hand-optimized for the mangling and no-mangling variants, which is why they are not converted. sysdeps/s390/s390-32/__longjmp.c and sysdeps/s390/s390-64/__longjmp.c are special: These are C sources, but most of the implementation is in assembler, so the PTR_DEMANGLE macro has to be undefined in some cases, to match the assembler style. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
* Introduce <pointer_guard.h>, extracted from <sysdep.h>Florian Weimer2022-10-185-0/+5
| | | | | | | | | | | | | | This allows us to define a generic no-op version of PTR_MANGLE and PTR_DEMANGLE. In the future, we can use PTR_MANGLE and PTR_DEMANGLE unconditionally in C sources, avoiding an unintended loss of hardening due to missing include files or unlucky header inclusion ordering. In i386 and x86_64, we can avoid a <tls.h> dependency in the C code by using the computed constant from <tcb-offsets.h>. <sysdep.h> no longer includes these definitions, so there is no cyclic dependency anymore when computing the <tcb-offsets.h> constants. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
* elf: Remove -fno-tree-loop-distribute-patterns usage on dl-supportAdhemerval Zanella2022-10-101-0/+29
| | | | | | | | | | | | | | Besides the option being gcc specific, this approach is still fragile and not future proof since we do not know if this will be the only optimization option gcc will add that transforms loops to memset (or any libcall). This patch adds a new header, dl-symbol-redir-ifunc.h, that can b used to redirect the compiler generated libcalls to port the generic memset implementation if required. Checked on x86_64-linux-gnu and aarch64-linux-gnu. Reviewed-by: Carlos O'Donell <carlos@redhat.com>
* elf: Remove _dl_string_hwcapJavier Pello2022-10-061-14/+0
| | | | | | | | Removal of legacy hwcaps support from the dynamic loader left no users of _dl_string_hwcap. Signed-off-by: Javier Pello <devel@otheo.eu> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
* Use atomic_exchange_release/acquireWilco Dijkstra2022-09-261-1/+1
| | | | | | | Rename atomic_exchange_rel/acq to use atomic_exchange_release/acquire since these map to the standard C11 atomic builtins. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
* s390: Move hwcaps/platform names out of _rtld_global_roFlorian Weimer2022-08-254-63/+43
| | | | | | | | | | | Changes to these arrays are often backported to stable releases, but additions to these arrays shift the offsets of the following _rltd_global_ro members, thus breaking the GLIBC_PRIVATE ABI. Obviously, this change is itself an internal ABI break, but at least it will avoid further ABI breaks going forward. Reviewed-by: Carlos O'Donell <carlos@redhat.com>
* S390: Fix werror=unused-variable in ifunc-impl-list.c.Stefan Liebler2022-08-181-1/+3
| | | | | | | | | | If the architecture level set is high enough, no IFUNCs are used at all and the variable i would be unused. Then the build fails with: ../sysdeps/s390/multiarch/ifunc-impl-list.c: In function ‘__libc_ifunc_impl_list’: ../sysdeps/s390/multiarch/ifunc-impl-list.c:76:10: error: unused variable ‘i’ [-Werror=unused-variable] 76 | size_t i = max; | ^ cc1: all warnings being treated as errors
* arc4random: simplify design for better safetyJason A. Donenfeld2022-07-273-624/+0
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Rather than buffering 16 MiB of entropy in userspace (by way of chacha20), simply call getrandom() every time. This approach is doubtlessly slower, for now, but trying to prematurely optimize arc4random appears to be leading toward all sorts of nasty properties and gotchas. Instead, this patch takes a much more conservative approach. The interface is added as a basic loop wrapper around getrandom(), and then later, the kernel and libc together can work together on optimizing that. This prevents numerous issues in which userspace is unaware of when it really must throw away its buffer, since we avoid buffering all together. Future improvements may include userspace learning more from the kernel about when to do that, which might make these sorts of chacha20-based optimizations more possible. The current heuristic of 16 MiB is meaningless garbage that doesn't correspond to anything the kernel might know about. So for now, let's just do something conservative that we know is correct and won't lead to cryptographic issues for users of this function. This patch might be considered along the lines of, "optimization is the root of all evil," in that the much more complex implementation it replaces moves too fast without considering security implications, whereas the incremental approach done here is a much safer way of going about things. Once this lands, we can take our time in optimizing this properly using new interplay between the kernel and userspace. getrandom(0) is used, since that's the one that ensures the bytes returned are cryptographically secure. But on systems without it, we fallback to using /dev/urandom. This is unfortunate because it means opening a file descriptor, but there's not much of a choice. Secondly, as part of the fallback, in order to get more or less the same properties of getrandom(0), we poll on /dev/random, and if the poll succeeds at least once, then we assume the RNG is initialized. This is a rough approximation, as the ancient "non-blocking pool" initialized after the "blocking pool", not before, and it may not port back to all ancient kernels, though it does to all kernels supported by glibc (≥3.2), so generally it's the best approximation we can do. The motivation for including arc4random, in the first place, is to have source-level compatibility with existing code. That means this patch doesn't attempt to litigate the interface itself. It does, however, choose a conservative approach for implementing it. Cc: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org> Cc: Florian Weimer <fweimer@redhat.com> Cc: Cristian Rodríguez <crrodriguez@opensuse.org> Cc: Paul Eggert <eggert@cs.ucla.edu> Cc: Mark Harris <mark.hsj@gmail.com> Cc: Eric Biggers <ebiggers@kernel.org> Cc: linux-crypto@vger.kernel.org Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
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