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author | John David Anglin <danglin@gcc.gnu.org> | 2022-02-22 17:28:46 +0000 |
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committer | John David Anglin <danglin@gcc.gnu.org> | 2022-02-22 17:28:46 +0000 |
commit | 9e7e5fda38471e00d1190479ea91d7b08ae3e304 (patch) | |
tree | 7a811ee404068f85a8bc877c029daaa1f04c0793 /sysdeps/unix/sysv/linux/hppa/getcontext.S | |
parent | fdc1ae67fef27eea1445bab4bdfe2f0fb3bc7aa1 (diff) | |
download | glibc-9e7e5fda38471e00d1190479ea91d7b08ae3e304.tar.gz glibc-9e7e5fda38471e00d1190479ea91d7b08ae3e304.tar.xz glibc-9e7e5fda38471e00d1190479ea91d7b08ae3e304.zip |
hppa: Revise gettext trampoline design
The current getcontext return trampoline is overly complex and it unnecessarily clobbers several registers. By saving the context pointer (r26) in the context, __getcontext_ret can restore any registers not restored by setcontext. This allows getcontext to save and restore the entire register context present when getcontext is entered. We use the unused oR0 context slot for the return from __getcontext_ret. While this is not directly useful in C, it can be exploited in assembly code. Registers r20, r23, r24 and r25 are not clobbered in the call path to getcontext. This allows a small simplification of swapcontext. It also allows saving and restoring the 6-bit SAR register in the LSB of the oSAR context slot. The getcontext flag value can be stored in the MSB of the oSAR slot.
Diffstat (limited to 'sysdeps/unix/sysv/linux/hppa/getcontext.S')
-rw-r--r-- | sysdeps/unix/sysv/linux/hppa/getcontext.S | 50 |
1 files changed, 27 insertions, 23 deletions
diff --git a/sysdeps/unix/sysv/linux/hppa/getcontext.S b/sysdeps/unix/sysv/linux/hppa/getcontext.S index 6470d73de5..dcdf986f2d 100644 --- a/sysdeps/unix/sysv/linux/hppa/getcontext.S +++ b/sysdeps/unix/sysv/linux/hppa/getcontext.S @@ -21,22 +21,28 @@ #include "ucontext_i.h" - /* Trampoline function. Non-standard calling ABI. */ + /* Trampoline function. Non-standard calling ABI. */ /* Can not use ENTRY(__getcontext_ret) here. */ .type __getcontext_ret, @function .hidden __getcontext_ret __getcontext_ret: .proc .callinfo FRAME=0,NO_CALLS - /* r26-r23 contain original r3-r6, but because setcontext - does not reload r3-r6 (it's using them as temporaries) - we must save them elsewhere and swap them back in. */ - copy %r23, %r3 - copy %r24, %r4 - copy %r25, %r5 - copy %r26, %r6 - /* r20 contains original return pointer. */ - bv 0(%r20) + /* Because setcontext does not reload r3-r6 (it's using them + as temporaries), we must load them ourself. */ + ldw oR3(%r26), %r3 + ldw oR4(%r26), %r4 + ldw oR5(%r26), %r5 + ldw oR6(%r26), %r6 + + /* Also reload registers clobbered by $$dyncall. */ + ldw oR21(%r26), %r21 + ldw oR22(%r26), %r22 + ldw oR31(%r26), %r31 + + /* oR0 contains original return pointer. */ + ldw oR0(%r26), %rp + bv 0(%rp) copy %r0, %ret0 .procend .size __getcontext_ret, .-__getcontext_ret @@ -64,13 +70,13 @@ ENTRY(__getcontext) stw %r17, oR17(%r26) stw %r18, oR18(%r26) stw %r19, oR19(%r26) - /* stw %r20, oR20(%r26) - used for trampoline. */ + stw %r20, oR20(%r26) stw %r21, oR21(%r26) stw %r22, oR22(%r26) - /* stw %r23, oR23(%r26) - used for trampoline. */ - /* stw %r24, oR24(%r26) - used for trampoline. */ - /* stw %r25, oR25(%r26) - used for trampoline. */ - /* stw %r26, oR26(%r26) - used for trampoline. */ + stw %r23, oR23(%r26) + stw %r24, oR24(%r26) + stw %r25, oR25(%r26) + stw %r26, oR26(%r26) stw %r27, oR27(%r26) stw %r28, oR28(%r26) stw %r29, oR29(%r26) @@ -89,7 +95,10 @@ ENTRY(__getcontext) stw %r0, oIASQ1(%r26) stw %r0, oIAOQ0(%r26) stw %r0, oIAOQ1(%r26) - stw %r0, oSAR(%r26) /* used as flag in swapcontext(). */ + + /* Save SAR register. */ + mfctl %sar, %r1 + stw %r1, oSAR(%r26) /* MSB used as flag in swapcontext(). */ /* Store floating-point regs. */ @@ -141,13 +150,8 @@ ENTRY(__getcontext) .cfi_offset 29, 4 /* Set up the trampoline registers. - r20, r23, r24, r25, r26 and r2 are clobbered - by call to getcontext() anyway. Reuse them. */ - stw %r2, oR20(%r26) - stw %r3, oR23(%r26) - stw %r4, oR24(%r26) - stw %r5, oR25(%r26) - stw %r6, oR26(%r26) + Use oR0 context slot to save return value. */ + stw %r2, oR0(%r26) #ifdef PIC addil LT%__getcontext_ret, %r19 ldw RT%__getcontext_ret(%r1), %r1 |