| From c0546e351f6d7ab50eb1de8cef1d0d167760fccc Mon Sep 17 00:00:00 2001 |
| From: Peter Korsgaard <peter@korsgaard.com> |
| Date: Mon, 27 Aug 2018 22:50:57 +0200 |
| Subject: [PATCH] bn_mul.h: fix x86 PIC inline ASM compilation with GCC < 5 |
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| |
| Fixes #1910 |
| |
| With ebx added to the MULADDC_STOP clobber list to fix #1550, the inline |
| assembly fails to build with GCC < 5 in PIC mode with the following error: |
| |
| include/mbedtls/bn_mul.h:46:13: error: PIC register clobbered by ‘ebx’ in ‘asm’ |
| |
| This is because older GCC versions treated the x86 ebx register (which is |
| used for the GOT) as a fixed reserved register when building as PIC. |
| |
| 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. |
| |
| https://www.gnu.org/software/gcc/gcc-5/changes.html |
| |
| As a workaround, detect this situation and disable the inline assembly, |
| similar to the MULADDC_CANNOT_USE_R7 logic. |
| |
| Upstream-Status: Backport [https://github.com/Mbed-TLS/mbedtls/commit/c0546e351f6d7ab50eb1de8cef1d0d167760fccc] |
| Signed-off-by: Peter Korsgaard <peter@korsgaard.com> |
| --- |
| library/bn_mul.h | 18 +++++++++++++++++- |
| 1 file changed, 17 insertions(+), 1 deletion(-) |
| |
| --- a/third_party/mbedtls/repo/include/mbedtls/bn_mul.h |
| +++ b/third_party/mbedtls/repo/include/mbedtls/bn_mul.h |
| @@ -55,12 +55,28 @@ |
| ( !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_INIT \ |
| asm( \ |