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authorMaciej W. Rozycki <macro@codesourcery.com>2013-09-09 22:36:57 +0100
committerMaciej W. Rozycki <macro@codesourcery.com>2013-09-09 22:36:57 +0100
commit95e7cf295e449c0aec3d7a76f01907bf300106bf (patch)
treeaa626c4fbf2f591b73d27caf79c74c796d1dc672 /elf
parenta9f5ce099cb30fe6b8f2ba240cacffe7ecfbfef2 (diff)
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Fix static-binary lazy FPU context allocation
Long ago static startup did not parse the auxiliary vector and therefore
could not get at any `AT_FPUCW' tag to check whether upon FPU context
allocation the kernel would use a FPU control word setting different to
that provided by the `__fpu_control' variable.  Static startup therefore
always initialized the FPU control word, forcing immediate FPU context
allocation even for binaries that otherwise never used the FPU.

As from GIT commit f8f900ecb9096ec47f5b7bb7626e29223c69061a static
startup supports parsing the auxiliary vector, so now it can avoid
explicit initialization of the FPU control word, just as can dynamic
startup, in the usual case where the setting written to the FPU control
word would be the same as the kernel uses.  This defers FPU context
allocation until the binary itself actually pokes at the FPU.

Note that the `AT_FPUCW' tag is usually absent from the auxiliary vector
in which case _FPU_DEFAULT is assumed to be the kernel default.
Diffstat (limited to 'elf')
-rw-r--r--elf/dl-support.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/elf/dl-support.c b/elf/dl-support.c
index 5a082feb7a..2023bd031c 100644
--- a/elf/dl-support.c
+++ b/elf/dl-support.c
@@ -167,6 +167,9 @@ size_t _dl_phnum;
 uint64_t _dl_hwcap __attribute__ ((nocommon));
 uint64_t _dl_hwcap2 __attribute__ ((nocommon));
 
+/* The value of the FPU control word the kernel will preset in hardware.  */
+fpu_control_t _dl_fpu_control = _FPU_DEFAULT;
+
 /* This is not initialized to HWCAP_IMPORTANT, matching the definition
    of _dl_important_hwcaps, below, where no hwcap strings are ever
    used.  This mask is still used to mediate the lookups in the cache
@@ -253,6 +256,9 @@ _dl_aux_init (ElfW(auxv_t) *av)
       case AT_HWCAP2:
 	GLRO(dl_hwcap2) = (unsigned long int) av->a_un.a_val;
 	break;
+      case AT_FPUCW:
+	GLRO(dl_fpu_control) = av->a_un.a_val;
+	break;
 #ifdef NEED_DL_SYSINFO
       case AT_SYSINFO:
 	GL(dl_sysinfo) = av->a_un.a_val;