On Saturday 19 November 2022 11:53:28 Pali Rohár wrote: > On Saturday 19 November 2022 17:12:12 LIU Hao wrote: > > 在 2022-11-18 23:40, Pali Rohár 写道: > > > GNU LD provides __ImageBase symbol since 2.19. This is standard windows > > > symbol and should be used instead of custom gnu _image_base__ symbol. > > > > > > For compatibility with older GNU LD versions, define __ImageBase as weak > > > alias to _image_base__ symbol. > > > > > > This allows to remove all #ifdef hacks for older GNU LD versions as with > > > this change __ImageBase works correctly with all GNU LD versions. > > > --- > > > > Generally speaking, one shouldn't use weak symbols when targeting Windows. I > > haven't investigated though, but many times weak symbols result in null or > > faulty addresses. > > Interesting, I did not know that there are issues with weak symbols. All > my tests with weak symbols passed, I have not spotted any issue. > > > Thus, weak symbols are unacceptable; but removal of references to > > `__image_base__` seems fine, if dropping support for binutils 2.18 is > > acceptable. BTW 2.19 was released in 2008 [1]. > > > > [1] https://lists.gnu.org/archive/html/info-gnu/2008-10/msg00014.html > > Another option is to detect at ./configure time if linker accepts > __ImageBase symbol. And if not then define __ImageBase as normal > (non-weak) symbol. Should be pretty simple.
Here is that variant without weak symbols. I have tested that it correctly generate helper symbol __ImageBase for older ld version 2.18. And for new ld version, file __imagebase.c is not compiled at all. diff --git a/mingw-w64-crt/Makefile.am b/mingw-w64-crt/Makefile.am index 2056b344dd3e..28d74c66a581 100644 --- a/mingw-w64-crt/Makefile.am +++ b/mingw-w64-crt/Makefile.am @@ -129,6 +129,10 @@ src_libmingw32=include/oscalls.h include/internal.h include/sect_attribs.h \ crt/tlsthrd.c crt/tlsmthread.c crt/tlsmcrt.c \ crt/cxa_atexit.c crt/cxa_thread_atexit.c crt/tls_atexit.c +if !LD_PROVIDES_IMAGEBASE +src_libmingw32+=crt/__imagebase.c +endif + src_libscrnsave=libsrc/scrnsave.c src_libscrnsavw=libsrc/scrnsave.c src_libstrmiids=libsrc/strmiids.c diff --git a/mingw-w64-crt/configure.ac b/mingw-w64-crt/configure.ac index 5c68ff967ba7..a0db980d7e0e 100644 --- a/mingw-w64-crt/configure.ac +++ b/mingw-w64-crt/configure.ac @@ -368,6 +368,12 @@ AC_MSG_RESULT([$enable_tests_unicode]) #AC_FUNC_VPRINTF #AC_CHECK_FUNCS([alarm atexit btowc fesetround floor ftruncate gettimeofday isascii localeconv mbrlen memmove memset pow rint setlocale sqrt strcasecmp strchr strncasecmp strtoull strtoumax]) +# Check for __ImageBase linker symbols. +AC_MSG_CHECKING([whether the linker provides __ImageBase symbol]) +AC_LINK_IFELSE([AC_LANG_PROGRAM([[extern unsigned char __ImageBase[];]], [[return __ImageBase[0];]])], [ld_provides_imagebase=yes], [ld_provides_imagebase=no]) +AC_MSG_RESULT([$ld_provides_imagebase]) +AM_CONDITIONAL([LD_PROVIDES_IMAGEBASE],[test $ld_provides_imagebase = yes]) + AC_CHECK_HEADER([_mingw_mac.h], [], [AC_MSG_ERROR([Please check if the mingw-w64 header set and the build/host option are set properly.])]) #Warnings and errors, default level is 3 diff --git a/mingw-w64-crt/crt/__imagebase.c b/mingw-w64-crt/crt/__imagebase.c new file mode 100644 index 000000000000..95715f953a61 --- /dev/null +++ b/mingw-w64-crt/crt/__imagebase.c @@ -0,0 +1,18 @@ +/** + * This file has no copyright assigned and is placed in the Public Domain. + * This file is part of the mingw-w64 runtime package. + * No warranty is given; refer to the file DISCLAIMER.PD within this package. + */ +#include <_mingw_mac.h> + +/* This file defines __ImageBase symbol for backward compatibility with older + * linker versions which do not provide this symbol. It is used only when linker + * does not provide this symbol (detected by ./configure). __ImageBase symbol is + * defined as alias to _image_base__ symbol which is provided by older linker + * versions. Note that gcc does not allow declaring global variable as alias to + * external symbol, so do it via inline assembly which allows it. */ +#define ASM_SYM(sym) __MINGW64_STRINGIFY(__MINGW_USYMBOL(sym)) +asm ( +".globl\t" ASM_SYM(__ImageBase) "\n\t" +".set\t" ASM_SYM(__ImageBase) "," ASM_SYM(_image_base__) +); _______________________________________________ Mingw-w64-public mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/mingw-w64-public
