Hi Yann, Yann Sionneau wrote, > This patch fixes segfault of all user space processes (including init, which > caused a panic) on recent buildroot powerpc32 builds. > > The issue has been reported by Romain Naour in this thread: > https://mailman.uclibc-ng.org/pipermail/devel/2021-May/002068.html > > Recent buildroot toolchain enables secure PLT in powerpc gcc. > The latter will then supply -msecure-plt to gas invocations by default. > Recent buildroot also enables PIE by defaults. > > For the secure PLT to work in PIC, the r30 register needs to point to the GOT. > Old "bss plt" was just a one-instruction-wide PLT slot, pointed-to by a > R_PPC_JMP_SLOT relocation, which was written on-the-fly to contain a branch > instruction to the correct address. It therefore had to stay writable. > New secure PLT only contains read-only code which loads the branch address > from the writable GOT. > > Note: secure PLT without PIC does not need r30 to be set. Because offset > between plt stub code and got is known at link-time. In this case the PLT > entry looks like: > 1009b3e0 <__uClibc_main@plt>: > 1009b3e0: 3d 60 10 0e lis r11,4110 > 1009b3e4: 81 6b 03 74 lwz r11,884(r11) > 1009b3e8: 7d 69 03 a6 mtctr r11 > 1009b3ec: 4e 80 04 20 bctr > > Whereas secure PLT with PIC - offset between plt and got is unknown at > link-time - looks like this: > 000af800 <00000000.plt_pic32.__uClibc_main>: > af800: 81 7e 03 80 lwz r11,896(r30) > af804: 7d 69 03 a6 mtctr r11 > af808: 4e 80 04 20 bctr > af80c: 60 00 00 00 nop > > Signed-off-by: Yann Sionneau <y...@sionneau.net>
Thanks, applied and pushed. best regards Waldemar _______________________________________________ devel mailing list devel@uclibc-ng.org https://mailman.uclibc-ng.org/cgi-bin/mailman/listinfo/devel
