Re: [uclibc-ng-devel] [PATCH] powerpc: fix builds with newer gcc/binutils which use secureplt by default

From: Yann Sionneau <yann(a)sionneau.net> This patch fixes segfault of all user space processes (including init, which caused a panic) on recent buildroot powerpc32 builds.

Recent buildroot toolchain enables secure PLT in powerpc gcc. The latter will then supply -msecure-plt to gas invocations by default.

For the secure PLT to work, 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.

Signed-off-by: Yann Sionneau &lt;yann(a)sionneau.net&gt; --- Rules.mak | 4 +++- ldso/ldso/powerpc/dl-startup.h | 3 +++ libc/sysdeps/linux/powerpc/crt1.S | 5 ++++- 3 files changed, 10 insertions(+), 2 deletions(-) diff --git a/Rules.mak b/Rules.mak index 1fa09be23..0ab41e800 100644 --- a/Rules.mak +++ b/Rules.mak @@ -58,6 +58,7 @@ LD = $(CROSS_COMPILE)ld NM = $(CROSS_COMPILE)nm OBJDUMP = $(CROSS_COMPILE)objdump STRIPTOOL = $(CROSS_COMPILE)strip +READELF = $(CROSS_COMPILE)readelf INSTALL = install LN = ln @@ -483,9 +484,10 @@ ifeq ($(TARGET_ARCH),powerpc) PICFLAG:=-fpic PIEFLAG_NAME:=-fpie PPC_HAS_REL16:=$(shell printf "\t.text\n\taddis 11,30,_GLOBAL_OFFSET_TABLE_-.@ha\n" | $(CC) -c -x assembler -o /dev/null - 2> /dev/null && echo -n y || echo -n n) + PPC_HAS_SECUREPLT:=$(shell tmpfile=$$(mktemp); printf '\#include <stdio.h>\nint main(void) { puts("hello"); return 0;}' > $${tmpfile}.c; $(CC) -x c $${tmpfile}.c -o $${tmpfile}; $(READELF) -d $${tmpfile} | grep PPC_GOT > /dev/null && echo -n y || echo -n n; rm $${tmpfile}.c $${tmpfile}) + CPU_CFLAGS-$(PPC_HAS_SECUREPLT) += -DPPC_HAS_SECUREPLT CPU_CFLAGS-$(PPC_HAS_REL16)+= -DHAVE_ASM_PPC_REL16 CPU_CFLAGS-$(CONFIG_E500) += "-D__NO_MATH_INLINES" - endif ifeq ($(TARGET_ARCH),bfin) diff --git a/ldso/ldso/powerpc/dl-startup.h b/ldso/ldso/powerpc/dl-startup.h index 8b2a517e2..7749395eb 100644 --- a/ldso/ldso/powerpc/dl-startup.h +++ b/ldso/ldso/powerpc/dl-startup.h @@ -25,6 +25,9 @@ __asm__( #else " bl _GLOBAL_OFFSET_TABLE_-4@local\n" /* Put our GOT pointer in r31, */ " mflr 31\n" +#endif +#ifdef PPC_HAS_SECUREPLT + " mr 30,31\n" #endif " addi 1,1,16\n" /* Restore SP */ " lwz 7,_dl_skip_args@got(31)\n" /* load EA of _dl_skip_args */ diff --git a/libc/sysdeps/linux/powerpc/crt1.S b/libc/sysdeps/linux/powerpc/crt1.S index 27bfc5a5a..78b946ad6 100644 --- a/libc/sysdeps/linux/powerpc/crt1.S +++ b/libc/sysdeps/linux/powerpc/crt1.S @@ -47,7 +47,7 @@ _start: mr r9,r1 /* Save the stack pointer and pass it to __uClibc_main */ clrrwi r1,r1,4 /* Align stack ptr to 16 bytes */ -#ifdef __PIC__ +#if defined(__PIC__) || defined(PPC_HAS_SECUREPLT) # ifdef HAVE_ASM_PPC_REL16 bcl 20,31,1f 1: mflr r31 @@ -57,6 +57,9 @@ _start: bl _GLOBAL_OFFSET_TABLE_-4@local mflr r31 # endif +#endif +#ifdef PPC_HAS_SECUREPLT + mr 30,31 #endif /* Set up the small data pointer in r13. */ #ifdef __PIC__