On 19 June 2018 at 07:07, Guenter Roeck <li...@roeck-us.net> wrote:
Modern assemblers may take the ISA into account when resolving local
symbols. This can result in bad address calculations when using badr
in the wrong location since the offset + 1 may be added twice, resulting
in an even address target for THUMB instructions. This in turn results
in an exception at (destination address + 2).
Unhandled exception: IPSR = 00000006 LR = fffffff1
CPU: 0 PID: 1 Comm: init Not tainted 4.18.0-rc1-00026-gf773e5bdf0c9 #15
Hardware name: MPS2 (Device Tree Support)
PC is at ret_fast_syscall+0x2/0x58
LR is at tty_ioctl+0x2a5/0x528
pc : [<21009002>] lr : [<210d1535>] psr: 4000000b
sp : 21825fa8 ip : 0000001c fp : 21a95892
r10: 00000000 r9 : 21824000 r8 : 210091c0
r7 : 00000036 r6 : 21ae1ee0 r5 : 00000000 r4 : 21ae1f3c
r3 : 00000000 r2 : 3d9adc25 r1 : 00000000 r0 : 00000000
xPSR: 4000000b
CPU: 0 PID: 1 Comm: init Not tainted 4.18.0-rc1-00026-gf773e5bdf0c9 #15
Hardware name: MPS2 (Device Tree Support)
[<2100bd8d>] (unwind_backtrace) from [<2100b13b>] (show_stack+0xb/0xc)
[<2100b13b>] (show_stack) from [<2100b87b>] (__invalid_entry+0x4b/0x4c)
Fix the problem by using a logical or instead of an addition. This is
less efficient but guaranteed to work.
Signed-off-by: Guenter Roeck <li...@roeck-us.net>
---
RFC: I don't really like this, but my ARM assembler knowledge is quite
limited. Just dropping the "+ 1" from badr doesn't work because some
other code needs it (the image hangs completely if I try that).
Ultimately I don't even know if the invoke_syscall macro should just
have used adr instead of badr (but then how did this ever work ?).
Seen with various toolchains based on gcc 7.x and binutils 2.30 when
building and testing MPS2 images.
Hello Guenter,
This issue has been discussed before. It appears the binutils people
suddenly started caring about the thumb annotation of local function
symbols, resulting in behavior that is not backwards compatible.
https://marc.info/?l=linux-arm-kernel&m=151143776213636&w=2
https://sourceware.org/bugzilla/show_bug.cgi?id=21458
Can you try the fix below please?
arch/arm/include/asm/assembler.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index 0cd4dccbae78..24c87ff2060f 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -195,7 +195,8 @@
.irp c,,eq,ne,cs,cc,mi,pl,vs,vc,hi,ls,ge,lt,gt,le,hs,lo
.macro badr\c, rd, sym
#ifdef CONFIG_THUMB2_KERNEL
- adr\c \rd, \sym + 1
+ adr\c \rd, \sym
+ orr \rd, #1
#else
adr\c \rd, \sym
#endif
--
2.7.4
----------8<------------
From: Ard Biesheuvel <ard.biesheu...@linaro.org>
Date: Tue, 16 Jan 2018 12:12:45 +0000
Subject: [PATCH] ARM: assembler: prevent ADR from setting the Thumb bit twice
To work around recent issues where ADR references to Thumb function
symbols may or may not have the Thumb bit set already when they are
resolved by GAS, reference the symbol indirectly via a local symbol
typed as 'object', stripping the ARM/Thumb annotation.
Signed-off-by: Ard Biesheuvel <ard.biesheu...@linaro.org>
diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index 6ae42ad29518..dd2ff94ad90b 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -195,13 +195,19 @@
.irp c,,eq,ne,cs,cc,mi,pl,vs,vc,hi,ls,ge,lt,gt,le,hs,lo
.macro badr\c, rd, sym
#ifdef CONFIG_THUMB2_KERNEL
- adr\c \rd, \sym + 1
+ __badr \c, \rd, \sym
#else
adr\c \rd, \sym
#endif
.endm
.endr
+ /* this needs to be a separate macro or \@ does not work correctly */
+ .macro __badr, c, rd, sym
+ .eqv .Lsym\@, \sym
+ adr\c \rd, .Lsym\@ + 1
