On 5 October 2016 at 15:48, Laszlo Ersek <ler...@redhat.com> wrote: > On 10/05/16 03:30, Yonghong Zhu wrote: >> Update the tools_def.template to add NOOPT support with GCC tool chains. >> >> Cc: Liming Gao <liming....@intel.com> >> Cc: Laszlo Ersek <ler...@redhat.com> >> Contributed-under: TianoCore Contribution Agreement 1.0 >> Signed-off-by: Yonghong Zhu <yonghong....@intel.com> >> --- >> BaseTools/Conf/tools_def.template | 28 ++++++++++++++++++++++++++++ >> 1 file changed, 28 insertions(+) > > I thought I understood what was going on, but apparently I was wrong > about that. > > In this patch, we add or modify: > - NOOPT_*_*_OBJCOPY_ADDDEBUGFLAG -- okay > - NOOPT_GCC*_(IA32|X64|ARM|AARCH64)_CC_FLAGS -- okay > > So that part is fine with me. But then we also add / modify: > - NOOPT_GCC(49|5)_AARCH64_DLINK_(FLAGS|XIPFLAGS) > - NOOPT_GCC5_ARM_DLINK_FLAGS > > First I thought the latter set of changes was unnecessary, because "ld" > didn't use "-O". I checked the manual, and I was wrong: "ld" does know / > use "-O". So those changes are fine, I guess. >
Yes, especially under LTO, in which case code generation is performed during the link stage, which should adhere to the same rules as the compiler. This not only applies to -O, but also to things like -march/-mcpu and -mstrict-align. This is why we pass all CFLAGS to the linker for the GCC5 LTO builds. > But then: is the patch *complete*? Because I can see some more DLINK > stuff, for IA32 and X64 (not just ARM and AARCH64). Is it okay to ignore > those? For example: > > *_GCC5_IA32_DLINK_FLAGS = DEF(GCC5_IA32_X64_DLINK_FLAGS) -Os > -Wl,-m,elf_i386,--oformat=elf32-i386 > > > *_GCC5_X64_DLINK_FLAGS = DEF(GCC5_X64_DLINK_FLAGS) -Os > > Where GCC5_X64_DLINK_FLAGS and GCC5_IA32_X64_DLINK_FLAGS even include > -flto. (I don't know if "-flto" hampers source level debugging or not.) > The GCC man page documents -flto as being a bad idea, i.e., """ Link-time optimization does not work well with generation of debugging information. Combining -flto with -g is currently experimental and expected to produce unexpected results. """ (which raises a philosophical question as well, i.e., to which extent expected unexpected results are still unexpected results. But I digress ...) Another note: the DEBUG build for ARM and AARCH64 is essentially NOOPT already, not DEBUG. How does this patch intend to deal with that? _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
