В Sat, 16 Nov 2013 14:17:51 +0100 Vladimir 'φ-coder/phcoder' Serbinenko <phco...@gmail.com> пишет:
> On 16.11.2013 14:00, Leif Lindholm wrote: > > On Sat, Nov 16, 2013 at 01:49:51PM +0100, Vladimir 'φ-coder/phcoder' > > Serbinenko wrote: > >> On 16.11.2013 13:39, Leif Lindholm wrote: > >>> - str r9, transition_space + 8 > >> You need to save r9. Otherwise GRUB will crash if compiled with clang. > > > > Hmm, but this is a bug in clang in that case. > > > > From an ABI perspective, grub_uboot_syscall is a veneer: > > the only visible side effect it is permitted to have is to corrupt r12. > > > According to wikipedia: > "Subroutines must preserve the contents of r4 to r11 and the stack pointer." According to ARM ABI documentation "A subroutine must preserve the contents of the registers r4 - r8, r10, r11 and SP (and r9 in PCS variants that designate r9 as v6)." So it sounds like whether r9 is preserved depends on platform. > So changing r9 sounds to me like this is actually U-Boot bug and > preserving it sounds like right way to handle it. > What's the harm in preserving r9? Is it used for something in calling? > > We need to additionally switch r8 between grub and u-boot copy because > > u-boot uses it for its global data pointer, and lr because we need to > > corrupt it to make u-boot return to this veneer to switch the r8 back > > again. > > > > This veneer should not touch anything else - so if we need to > > temporarily work around a toolchain ABI bug, can we do this via an > > ifdef and a config option? > > > If the bug is on clang side (I doubt it right now), there is no way to > handle it without side effects and we can invent a test for it, we can > reject buggy compilers (clang is secondary compiler) > > / > > Leif > > > > _______________________________________________ > > Grub-devel mailing list > > Grub-devel@gnu.org > > https://lists.gnu.org/mailman/listinfo/grub-devel > > > >
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