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new 65c6383f89 configure/x86: test 6- and 7-register inline asm
65c6383f89 is described below
commit 65c6383f899be853e6bed30797909073956e4745
Author: Kirill A. Korinsky <[email protected]>
AuthorDate: Wed Jun 24 21:00:53 2026 +0200
Commit: michaelni <[email protected]>
CommitDate: Sat Jul 18 23:09:32 2026 +0000
configure/x86: test 6- and 7-register inline asm
HAVE_6REGS and HAVE_7REGS should describe whether the compiler can
allocate the inline asm register sets they guard. The old x86-32 logic
inferred that from EBX/EBP availability, while x86-64 enabled both
macros without a configure test.
Probe the 6- and 7-register asm constraints directly for all x86 targets
and let asm.h use the configure results. Drop the EBP availability
probe, which is no longer used. Keep EBX availability, as other inline
asm still uses it to decide whether named EBX can be clobbered.
---
configure | 33 +++++++--------------------------
libavutil/x86/asm.h | 4 ++--
2 files changed, 9 insertions(+), 28 deletions(-)
diff --git a/configure b/configure
index e09bbd7f04..dc5192cc91 100755
--- a/configure
+++ b/configure
@@ -2636,7 +2636,6 @@ TOOLCHAIN_FEATURES="
as_object_arch
asm_mod_q
blocks_extension
- ebp_available
ebx_available
gnu_as
gnu_windres
@@ -2649,7 +2648,8 @@ TOOLCHAIN_FEATURES="
symver_asm_label
symver_gnu_asm
vfp_args
- x86_32_7regs
+ x86_6regs
+ x86_7regs
xform_asm
xmm_clobbers
"
@@ -6848,27 +6848,13 @@ elif enabled x86; then
check_builtin rdtsc intrin.h "__rdtsc()"
check_builtin mm_empty mmintrin.h "_mm_empty()"
- # check whether EBP is available on x86
- # As 'i' is stored on the stack, this program will crash
- # if the base pointer is used to access it because the
- # base pointer is cleared in the inline assembly code.
- check_exec_crash <<EOF && enable ebp_available
-volatile int i=0;
-__asm__ volatile ("xorl %%ebp, %%ebp" ::: "%ebp");
-return i;
-EOF
-
# check whether EBX is available on x86
check_inline_asm ebx_available '""::"b"(0)' &&
check_inline_asm ebx_available '"":::"%ebx"'
- # check whether 7 registers are available on x86-32
- # Since
https://github.com/llvm/llvm-project/commit/0d471b3f64d3116bd57c79d872f7384fff80daa5,
- # Clang can save/restore EBP around clobber-only asm, so the EBP
- # crash probe alone can be a false positive for 7-register asm.
- disable x86_32_7regs
- enabled_all x86_32 ebx_available ebp_available &&
- check_inline_asm x86_32_7regs '"" :: "r"(0), "r"(1), "r"(2), "r"(3),
"g"(4), "r"(5) : "%eax", "%edx"'
+ # check whether 6 and 7 registers are available on x86
+ check_inline_asm x86_6regs '"" :: "r"(0), "r"(1), "r"(2), "r"(3), "g"(4) :
"%eax", "%edx"'
+ check_inline_asm x86_7regs '"" :: "r"(0), "r"(1), "r"(2), "r"(3), "g"(4),
"r"(5) : "%eax", "%edx"'
# check whether xmm clobbers are supported
check_inline_asm xmm_clobbers '"":::"%xmm0"'
@@ -8125,8 +8111,6 @@ if enabled icc; then
# 11030: Warning unknown option --as-needed
# 10156: ignoring option '-export'; no argument required
check_ldflags -wd10156,11030
- # icc 11.0 and 11.1 work with ebp_available, but don't pass the test
- enable ebp_available
# The test above does not test linking
[ -n "$lto" ] && disable symver_asm_label
if enabled x86_32; then
@@ -8228,7 +8212,6 @@ elif enabled_any msvc icl; then
add_cflags -Qansi-alias
# Some inline asm is not compilable in debug
if enabled debug; then
- disable ebp_available
disable ebx_available
fi
fi
@@ -8494,10 +8477,8 @@ if enabled x86; then
echo "i686 features enabled ${i686-no}"
echo "CMOV is fast ${fast_cmov-no}"
echo "EBX available ${ebx_available-no}"
- echo "EBP available ${ebp_available-no}"
-fi
-if enabled x86_32; then
- echo "7 registers available ${x86_32_7regs-no}"
+ echo "6 registers available ${x86_6regs-no}"
+ echo "7 registers available ${x86_7regs-no}"
fi
if enabled aarch64; then
echo "NEON enabled ${neon-no}"
diff --git a/libavutil/x86/asm.h b/libavutil/x86/asm.h
index fc9f50b1a9..c304aa3279 100644
--- a/libavutil/x86/asm.h
+++ b/libavutil/x86/asm.h
@@ -71,8 +71,8 @@ typedef int32_t x86_reg;
typedef int x86_reg;
#endif
-#define HAVE_7REGS (ARCH_X86_64 || HAVE_X86_32_7REGS)
-#define HAVE_6REGS (ARCH_X86_64 || (HAVE_EBX_AVAILABLE || HAVE_EBP_AVAILABLE))
+#define HAVE_7REGS HAVE_X86_7REGS
+#define HAVE_6REGS HAVE_X86_6REGS
#if ARCH_X86_64 && defined(PIC)
# define BROKEN_RELOCATIONS 1
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