On 3/5/20 6:13 PM, Sasha Levin wrote: > From: Victor Kamensky <kamensky@xxxxxxxxx> > > [ Upstream commit d3f703c4359ff06619b2322b91f69710453e6b6d ] > > Observed that when kernel is built with Yocto mips64-poky-linux-gcc, > and mips64-poky-linux-gnun32-gcc toolchain, resulting vdso contains > 'jalr t9' instructions in its code and since in vdso case nobody > sets GOT table code crashes when instruction reached. On other hand > observed that when kernel is built mips-poky-linux-gcc toolchain, the > same 'jalr t9' instruction are replaced with PC relative function > calls using 'bal' instructions. > > The difference boils down to -mrelax-pic-calls and -mexplicit-relocs > gcc options that gets different default values depending on gcc > target triplets and corresponding binutils. -mrelax-pic-calls got > enabled by default only in mips-poky-linux-gcc case. MIPS binutils > ld relies on R_MIPS_JALR relocation to convert 'jalr t9' into 'bal' > and such relocation is generated only if -mrelax-pic-calls option > is on. > > Please note 'jalr t9' conversion to 'bal' can happen only to static > functions. These static PIC calls use mips local GOT entries that > are supposed to be filled with start of DSO value by run-time linker > (missing in VDSO case) and they do not have dynamic relocations. > Global mips GOT entries must have dynamic relocations and they should > be prevented by cmd_vdso_check Makefile rule. > > Solution call out -mrelax-pic-calls and -mexplicit-relocs options > explicitly while compiling MIPS vdso code. That would get correct > and consistent between different toolchains behaviour. > > Reported-by: Bruce Ashfield <bruce.ashfield@xxxxxxxxx> > Signed-off-by: Victor Kamensky <kamensky@xxxxxxxxx> > Signed-off-by: Paul Burton <paulburton@xxxxxxxxxx> > Cc: linux-mips@xxxxxxxxxxxxxxx > Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx> > Cc: James Hogan <jhogan@xxxxxxxxxx> > Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> > Cc: richard.purdie@xxxxxxxxxxxxxxxxxxx > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> > --- > arch/mips/vdso/Makefile | 1 + > 1 file changed, 1 insertion(+) > Hi Sasha, Why was this not added to the 5.4 stable branch? Some OpenWrt users ran into this problem with kernel 5.4 on MIPS64 [0]. We backported this patch on our own in OpenWrt [1], but it should be added to the sable branch in my opinion as it fixes a real problem. @Sasha: Can you add it to the 5.4 stable branch or should I send some special email? [0]: https://bugs.openwrt.org/index.php?do=details&task_id=3277 [1]: https://git.openwrt.org/2932b4d05e1d212259c2903fd9cebcee5616680b Hauke
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