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new b57ff00bcf configure/x86: split 7-register check from EBP availability
b57ff00bcf is described below
commit b57ff00bcf485ad06b1619d31499a6db27a636b0
Author: Kirill A. Korinsky <[email protected]>
AuthorDate: Fri Jun 19 23:31:20 2026 +0200
Commit: michaelni <[email protected]>
CommitDate: Sat Jun 20 11:46:49 2026 +0000
configure/x86: split 7-register check from EBP availability
LLVM commit
https://github.com/llvm/llvm-project/commit/0d471b3f64d3116bd57c79d872f7384fff80daa5
made Clang save and restore EBP around inline asm that only
clobbers it. This can make the existing EBP crash probe pass even
when the compiler still cannot allocate the 7-register i386 inline
asm used behind HAVE_7REGS.
Keep ebp_available for HAVE_6REGS and add a separate
x86_32_7regs probe for HAVE_7REGS.
Discussion:
https://marc.info/?t=178015389900001&r=1&w=2
---
configure | 12 ++++++++++++
libavutil/x86/asm.h | 2 +-
2 files changed, 13 insertions(+), 1 deletion(-)
diff --git a/configure b/configure
index db98f049ed..a6bbb86807 100755
--- a/configure
+++ b/configure
@@ -2656,6 +2656,7 @@ TOOLCHAIN_FEATURES="
symver_asm_label
symver_gnu_asm
vfp_args
+ x86_32_7regs
xform_asm
xmm_clobbers
"
@@ -6849,6 +6850,14 @@ EOF
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 xmm clobbers are supported
check_inline_asm xmm_clobbers '"":::"%xmm0"'
@@ -8509,6 +8518,9 @@ if enabled x86; then
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}"
+fi
if enabled aarch64; then
echo "NEON enabled ${neon-no}"
echo "DOTPROD enabled ${dotprod-no}"
diff --git a/libavutil/x86/asm.h b/libavutil/x86/asm.h
index f06ea25035..fc9f50b1a9 100644
--- a/libavutil/x86/asm.h
+++ b/libavutil/x86/asm.h
@@ -71,7 +71,7 @@ typedef int32_t x86_reg;
typedef int x86_reg;
#endif
-#define HAVE_7REGS (ARCH_X86_64 || (HAVE_EBX_AVAILABLE && HAVE_EBP_AVAILABLE))
+#define HAVE_7REGS (ARCH_X86_64 || HAVE_X86_32_7REGS)
#define HAVE_6REGS (ARCH_X86_64 || (HAVE_EBX_AVAILABLE || HAVE_EBP_AVAILABLE))
#if ARCH_X86_64 && defined(PIC)
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