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Merge pull request #1986 from jacmet/bn_mul-fix-x86-pic-compilation-for-gcc-4

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bn_mul.h: fix x86 PIC inline ASM compilation with GCC < 5
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Dave Rodgman 2022-07-21 17:34:48 +01:00 committed by GitHub
commit a948f0588c
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2 changed files with 21 additions and 1 deletions
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ChangeLog.d/bn_mul-fix-x86-pic-compilation-for-gcc-4.txt Normal file
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@ -0,0 +1,4 @@
Bugfix
* Fix a long-standing build failure when building x86 PIC code with old
gcc (4.x). The code will be slower, but will compile. We do however
recommend upgrading to a more recent compiler instead. Fixes #1910.

18
library/bn_mul.h
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@ -90,13 +90,29 @@
#if defined(__GNUC__) && \
( !defined(__ARMCC_VERSION) || __ARMCC_VERSION >= 6000000 )
/*
* GCC < 5.0 treated the x86 ebx (which is used for the GOT) as a
* fixed reserved register when building as PIC, leading to errors
* like: bn_mul.h:46:13: error: PIC register clobbered by 'ebx' in 'asm'
*
* This is fixed by an improved register allocator in GCC 5+. From the
* release notes:
* Register allocation improvements: Reuse of the PIC hard register,
* instead of using a fixed register, was implemented on x86/x86-64
* targets. This improves generated PIC code performance as more hard
* registers can be used.
*/
#if defined(__GNUC__) && __GNUC__ < 5 && defined(__PIC__)
#define MULADDC_CANNOT_USE_EBX
#endif
/*
* Disable use of the i386 assembly code below if option -O0, to disable all
* compiler optimisations, is passed, detected with __OPTIMIZE__
* This is done as the number of registers used in the assembly code doesn't
* work with the -O0 option.
*/
#if defined(__i386__) && defined(__OPTIMIZE__)
#if defined(__i386__) && defined(__OPTIMIZE__) && !defined(MULADDC_CANNOT_USE_EBX)
#define MULADDC_X1_INIT \
{ mbedtls_mpi_uint t; \