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." 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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