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authorMichael Ellerman <mpe@ellerman.id.au>2021-07-29 14:56:36 +0200
committerMichael Ellerman <mpe@ellerman.id.au>2021-07-29 15:13:12 +0200
commita88603f4b92ecef9e2359e40bcb99ad399d85dd7 (patch)
treec81294374114b8e8cf033db188be2f6ccf2ba38b
parentpowerpc/pseries: Fix regression while building external modules (diff)
downloadlinux-a88603f4b92ecef9e2359e40bcb99ad399d85dd7.tar.xz
linux-a88603f4b92ecef9e2359e40bcb99ad399d85dd7.zip
powerpc/vdso: Don't use r30 to avoid breaking Go lang
The Go runtime uses r30 for some special value called 'g'. It assumes that value will remain unchanged even when calling VDSO functions. Although r30 is non-volatile across function calls, the callee is free to use it, as long as the callee saves the value and restores it before returning. It used to be true by accident that the VDSO didn't use r30, because the VDSO was hand-written asm. When we switched to building the VDSO from C the compiler started using r30, at least in some builds, leading to crashes in Go. eg: ~/go/src$ ./all.bash Building Go cmd/dist using /usr/lib/go-1.16. (go1.16.2 linux/ppc64le) Building Go toolchain1 using /usr/lib/go-1.16. go build os/exec: /usr/lib/go-1.16/pkg/tool/linux_ppc64le/compile: signal: segmentation fault go build reflect: /usr/lib/go-1.16/pkg/tool/linux_ppc64le/compile: signal: segmentation fault go tool dist: FAILED: /usr/lib/go-1.16/bin/go install -gcflags=-l -tags=math_big_pure_go compiler_bootstrap bootstrap/cmd/...: exit status 1 There are patches in flight to fix Go[1], but until they are released and widely deployed we can workaround it in the VDSO by avoiding use of r30. Note this only works with GCC, clang does not support -ffixed-rN. 1: https://go-review.googlesource.com/c/go/+/328110 Fixes: ab037dd87a2f ("powerpc/vdso: Switch VDSO to generic C implementation.") Cc: stable@vger.kernel.org # v5.11+ Reported-by: Paul Menzel <pmenzel@molgen.mpg.de> Tested-by: Paul Menzel <pmenzel@molgen.mpg.de> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20210729131244.2595519-1-mpe@ellerman.id.au
-rw-r--r--arch/powerpc/kernel/vdso64/Makefile7
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile
index 2813e3f98db6..3c5baaa6f1e7 100644
--- a/arch/powerpc/kernel/vdso64/Makefile
+++ b/arch/powerpc/kernel/vdso64/Makefile
@@ -27,6 +27,13 @@ KASAN_SANITIZE := n
ccflags-y := -shared -fno-common -fno-builtin -nostdlib \
-Wl,-soname=linux-vdso64.so.1 -Wl,--hash-style=both
+
+# Go prior to 1.16.x assumes r30 is not clobbered by any VDSO code. That used to be true
+# by accident when the VDSO was hand-written asm code, but may not be now that the VDSO is
+# compiler generated. To avoid breaking Go tell GCC not to use r30. Impact on code
+# generation is minimal, it will just use r29 instead.
+ccflags-y += $(call cc-option, -ffixed-r30)
+
asflags-y := -D__VDSO64__ -s
targets += vdso64.lds