我正在尝试在32位centos6上编译webrtc并收到以下错误。但这在64位数上运行良好。有人能帮助我吗？
row_gcc.cc:3574:4: error: ‘asm’ operand has impossible constraints
编译命令：
CXX obj/chromium/src/third_party/libyuv/source/libyuv.row_gcc.o
FAILED: obj/chromium/src/third_party/libyuv/source/libyuv.row_gcc.o
c++ -MMD -MF obj/chromium/src/third_party/libyuv/source/libyuv.row_gcc.o.d
-DV8_DEPRECATION_WARNINGS -D_FILE_OFFSET_BITS=64 -DCHROMIUM_BUILD
-DUI_COMPOSITOR_IMAGE_TRANSPORT -DUSE_AURA=1 -DUSE_PANGO=1 -DUSE_CAIRO=1
-DUSE_DEFAULT_RENDER_THEME=1 -DUSE_LIBJPEG_TURBO=1 -DUSE_X11=1
-DUSE_CLIPBOARD_AURAX11=1 -DENABLE_WEBRTC=1 -DENABLE_MEDIA_ROUTER=1
-DENABLE_PEPPER_CDMS -DENABLE_NOTIFICATIONS -DENABLE_TOPCHROME_MD=1
-DUSE_UDEV -DFIELDTRIAL_TESTING_ENABLED -DENABLE_TASK_MANAGER=1
-DENABLE_EXTENSIONS=1 -DENABLE_PDF=1 -DENABLE_PLUGINS=1
-DENABLE_SESSION_SERVICE=1 -DENABLE_THEMES=1 -DENABLE_PRINTING=1
-DENABLE_BASIC_PRINTING=1 -DENABLE_PRINT_PREVIEW=1 -DENABLE_SPELLCHECK=1
-DENABLE_CAPTIVE_PORTAL_DETECTION=1 -DENABLE_APP_LIST=1
-DENABLE_SETTINGS_APP=1 -DENABLE_SUPERVISED_USERS=1 -DENABLE_MDNS=1
-DENABLE_SERVICE_DISCOVERY=1 -DV8_USE_EXTERNAL_STARTUP_DATA
-DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD -DSAFE_BROWSING_DB_LOCAL
-DHAVE_JPEG -DUSE_LIBPCI=1 -DUSE_GLIB=1 -DUSE_NSS_CERTS=1
-D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS
-DDYNAMIC_ANNOTATIONS_ENABLED=1 -DWTF_USE_DYNAMIC_ANNOTATIONS=1
-D_DEBUG -Igen
-I../../chromium/src/third_party/libyuv/include
-I../../chromium/src/third_party/libyuv
-I../../chromium/src/third_party/libjpeg_turbo -fstack-protector
--param=ssp-buffer-size=4 -pthread -fno-strict-aliasing -Wall -Wno-extra
-Wno-unused-parameter -Wno-missing-field-initializers -fvisibility=hidden
-pipe -fPIC
-B/home/test/webrtc-checkout/src/third_party/binutils/Linux_ia32/Release/bin
-Wno-unused-local-typedefs -msse2 -mfpmath=sse -mmmx -m32 -O0 -g
-funwind-tables -fno-exceptions -fno-rtti -fno-threadsafe-statics
-fvisibility-inlines-hidden
-std=gnu++11 -Wno-narrowing
-c ../../chromium/src/third_party/libyuv/source/row_gcc.cc
-o obj/chromium/src/third_party/libyuv/source/libyuv.row_gcc.o
../../chromium/src/third_party/libyuv/source/row_gcc.cc:
In function ‘void libyuv::BlendPlaneRow_SSSE3(const uint8*,
const uint8*, const uint8*, uint8*, int)’:
../../chromium/src/third_party/libyuv/source/row_gcc.cc:3574:4:
error: ‘asm’ operand has impossible constraints
gcc版本：4.8.5
作为版本：GNU汇编程序（GNU Binutils）2.26.20160125
third_party/binutils/Linux_ia32/Release/bin/as --version
GNU assembler (GNU Binutils) 2.26.20160125
Copyright (C) 2015 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or later.
This program has absolutely no warranty.
This assembler was configured for a target of `i686-pc-linux-gnu'.
chrome / src / third_party / libyuv / source / row_gcc.cc中的代码：
void BlendPlaneRow_SSSE3(const uint8* src0, const uint8* src1,
const uint8* alpha, uint8* dst, int width) {
asm volatile (
"pcmpeqb %%xmm5,%%xmm5 \n"
"psllw $0x8,%%xmm5 \n"
"mov $0x80808080,%%eax \n"
"movd %%eax,%%xmm6 \n"
"pshufd $0x0,%%xmm6,%%xmm6 \n"
"mov $0x807f807f,%%eax \n"
"movd %%eax,%%xmm7 \n"
"pshufd $0x0,%%xmm7,%%xmm7 \n"
"sub %2,%0 \n"
"sub %2,%1 \n"
"sub %2,%3 \n"
// 8 pixel loop.
LABELALIGN
"1: \n"
"movq (%2),%%xmm0 \n"
"punpcklbw %%xmm0,%%xmm0 \n"
"pxor %%xmm5,%%xmm0 \n"
"movq (%0,%2,1),%%xmm1 \n"
"movq (%1,%2,1),%%xmm2 \n"
"punpcklbw %%xmm2,%%xmm1 \n"
"psubb %%xmm6,%%xmm1 \n"
"pmaddubsw %%xmm1,%%xmm0 \n"
"paddw %%xmm7,%%xmm0 \n"
"psrlw $0x8,%%xmm0 \n"
"packuswb %%xmm0,%%xmm0 \n"
"movq %%xmm0,(%3,%2,1) \n"
"lea 0x8(%2),%2 \n"
"sub $0x8,%4 \n"
"jg 1b \n"
: "+r"(src0), // %0
"+r"(src1), // %1
"+r"(alpha), // %2
"+r"(dst), // %3
"+r"(width) // %4
:: "memory", "cc", "eax", "xmm0", "xmm1", "xmm2", "xmm5", "xmm6", "xmm7"
);
答案 0 :(得分：3)
像大卫沃弗雷德所说，问题在于你已经没有注册。有8个通用寄存器，其中一个是ESP，堆栈指针，永远不能用于满足约束。由于您正在编译的选项，还可以使用另外两个寄存器EBP和EBX来满足约束条件。由于您在没有优化的情况下进行编译，因此EBP寄存器保留用于帧指针，并且因为您使用-fPIC标志，所以EBX寄存器被保留用于访问GOT（全局对象表） 。
因此，留下五个可用于满足寄存器约束的寄存器，EAX，ECX，EDX，ESI和EDI。然而，你的asm语句破坏了EAX，因此无法使用，只留下四个寄存器。 asm语句有五个具有寄存器约束的操作数，这意味着它需要五个独立的寄存器，但只有四个可供编译器使用。所以限制是不可能满足的。
一个简单的解决方案是通过在asm语句中删除EAX的使用来释放寄存器。该寄存器用于将两个不同的常量值加载到两个不同的XMM寄存器中。相反，它可以直接从内存加载常量。例如：
void BlendPlaneRow_SSSE3(const uint8* src0, const uint8* src1,
const uint8* alpha, uint8* dst, int width) {
static unsigned const __attribute__((aligned(4))) xmm6[4] = {
0x80808080, 0x80808080, 0x80808080, 0x80808080
};
static unsigned const __attribute__((aligned(4))) xmm7[4] = {
0x807f807f, 0x807f807f, 0x807f807f, 0x807f807f
};
asm volatile (
"pcmpeqb %%xmm5,%%xmm5 \n"
"psllw $0x8,%%xmm5 \n"
"movaps %5,%%xmm6 \n"
"movaps %6,%%xmm7 \n"
"sub %2,%0 \n"
"sub %2,%1 \n"
"sub %2,%3 \n"
// 8 pixel loop.
LABELALIGN
"1: \n"
"movq (%2),%%xmm0 \n"
"punpcklbw %%xmm0,%%xmm0 \n"
"pxor %%xmm5,%%xmm0 \n"
"movq (%0,%2,1),%%xmm1 \n"
"movq (%1,%2,1),%%xmm2 \n"
"punpcklbw %%xmm2,%%xmm1 \n"
"psubb %%xmm6,%%xmm1 \n"
"pmaddubsw %%xmm1,%%xmm0 \n"
"paddw %%xmm7,%%xmm0 \n"
"psrlw $0x8,%%xmm0 \n"
"packuswb %%xmm0,%%xmm0 \n"
"movq %%xmm0,(%3,%2,1) \n"
"lea 0x8(%2),%2 \n"
"sub $0x8,%4 \n"
"jg 1b \n"
: "+r"(src0), // %0
"+r"(src1), // %1
"+r"(alpha), // %2
"+r"(dst), // %3
"+r"(width) // %4
: "m" (xmm6),
"m" (xmm7)
: "memory", "cc", "xmm0", "xmm1", "xmm2", "xmm5", "xmm6", "xmm7"
);
}
更好的解决方案是重写它以使用内在函数并让编译器完成所有寄存器分配。