[PATCH 00/12] ARM: use adr_l/ldr_l macros for PC-relative references
Nick Desaulniers
ndesaulniers at google.com
Wed Sep 16 17:25:07 EDT 2020
On Wed, Sep 16, 2020 at 1:45 PM Ard Biesheuvel <ardb at kernel.org> wrote:
>
> On Wed, 16 Sep 2020 at 22:53, Nick Desaulniers <ndesaulniers at google.com> wrote:
> >
> > On Tue, Sep 15, 2020 at 10:55 PM Ard Biesheuvel <ardb at kernel.org> wrote:
> > >
> > > On Wed, 16 Sep 2020 at 02:31, Nick Desaulniers <ndesaulniers at google.com> wrote:
> > > >
> > > > On Tue, Sep 15, 2020 at 2:30 PM Ard Biesheuvel <ardb at kernel.org> wrote:
> > > > >
> > > > > Excellent, thanks for testing. Do you have any coverage for Thumb2
> > > > > builds as well? (CONFIG_THUMB2_KERNEL=y)
> > > >
> > > > Ah, right, manually testing ARCH=arm defconfig with
> > > > CONFIG_THUMB2_KERNEL enabled via menuconfig:
> > > >
> > > > Builds and boots for clang.
> > > >
> > > > (Also needed https://lore.kernel.org/lkml/20200915225751.274531-1-ndesaulniers@google.com/T/#u
> > > > for an unrelated issue).
> > > >
> > > > For GCC, I observe:
> > > >
> > > > arch/arm/vfp/vfphw.o: in function `vfp_support_entry':
> > > > (.text+0xa): relocation truncated to fit: R_ARM_THM_JUMP19 against
> > > > symbol `vfp_kmode_exception' defined in .text.unlikely section in
> > > > arch/arm/vfp/vfpmodule.o
> > > >
> > >
> > > Interesting. And this is using ld.bfd ?
> >
> > $ arm-linux-gnueabihf-ld --version
> > GNU ld (GNU Binutils for Debian) 2.34
> >
> > .text.unlikely reminds me of the sections created when profiling data
> > is present. That's obviously not the case here, so maybe there's
> > other ways this section can be created by GCC? I may have added a
> > patch recently for placing this section explicitly, which was a
> > prerequisite for Kees' series explicitly placing all sections.
> > https://lore.kernel.org/lkml/159896087937.20229.4955362311782724603.tip-bot2@tip-bot2/
> > Maybe that can be improved?
> >
> > IIRC, LLD is able to emit range extension thunks for these cases, but
> > BFD does not.
>
> ld.bfd will usually emit veneers for branches that turn out to be out
> of range in the final link stage.
>
> Does the following help?
>
> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S
> index 4fcff9f59947..f1468702fbc9 100644
> --- a/arch/arm/vfp/vfphw.S
> +++ b/arch/arm/vfp/vfphw.S
> @@ -82,6 +82,7 @@ ENTRY(vfp_support_entry)
> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions
> and r3, r3, #MODE_MASK @ are supported in kernel mode
> teq r3, #USR_MODE
> +THUMB( it ne )
> bne vfp_kmode_exception @ Returns through lr
>
> VFPFMRX r1, FPEXC @ Is the VFP enabled?
Yes, it does! I'm curious why though? I've seen the "it prefixes"
before (is that what they're called?), but I don't recall what they're
for. How come that solves this issue?
(Feel free to use my tested by tag on a subsequent resulting patch
that uses that). That fix is irrespective of this series, so you
should send it maybe separately?
Also, it looks like the GCC build of milbeaut_m10v_defconfig fails to
boot for me in QEMU; so maybe not just a Clang bug (or maybe, more
than one bug). (or maybe one of my command line params to QEMU is
wrong).
Stepping through start_kernel(), the call to setup_arch() seems to
hang in qemu. For both GCC and Clang builds. A breakpoint in panic()
never gets hit. Looks like the deepest I can get is:
Looks like:
#0 memblock_alloc_try_nid (size=108, align=4, min_addr=0, max_addr=0,
nid=-1) at mm/memblock.c:1601
#1 0xc060f0b4 in memblock_alloc (size=<optimized out>,
align=<optimized out>) at ./include/linux/memblock.h:409
#2 cma_init_reserved_mem (base=1543503872, size=67108864,
order_per_bit=0, name=0xc04b9240 "reserved", res_cma=0xc07ccbdc
<dma_contiguous_default_area>) at mm/cma.c:190
#3 0xc060f2c0 in cma_declare_contiguous_nid (base=1543503872,
size=67108864, limit=1610612736, alignment=8388608, order_per_bit=0,
fixed=false, name=0xc04b9240 "reserved",
res_cma=0xc07ccbdc <dma_contiguous_default_area>, nid=-1) at mm/cma.c:352
#4 0xc0608cb6 in cma_declare_contiguous (alignment=<optimized out>,
order_per_bit=<optimized out>, name=<optimized out>,
res_cma=<optimized out>, fixed=<optimized out>,
limit=<optimized out>, size=<optimized out>, base=<optimized out>)
at ./include/linux/cma.h:28
#5 dma_contiguous_reserve_area (size=<optimized out>, base=<optimized
out>, limit=<optimized out>, res_cma=0xc07ccbdc
<dma_contiguous_default_area>, fixed=false)
at kernel/dma/contiguous.c:201
#6 0xc0608d22 in dma_contiguous_reserve (limit=<optimized out>) at
kernel/dma/contiguous.c:171
#7 0xc0604584 in arm_memblock_init (mdesc=0xc061bfe8
<__mach_desc_GENERIC_DT.35641>) at arch/arm/mm/init.c:230
#8 0xc060302c in setup_arch (cmdline_p=<optimized out>) at
arch/arm/kernel/setup.c:1132
#9 0xc06007d2 in start_kernel () at init/main.c:857
there's a call to memset that seems to hang. I wonder if memset() was
defined in terms of __builtin_memset, which oft can result in infinite
loops? (IIRC there's an AEABI related memset; this kind of thing has
hit android userspace before).
(gdb) layout asm
shows that the source call to memset is transformed into a call to mmioset.
(gdb) bt
#0 mmioset () at arch/arm/lib/memset.S:19
#1 0xc060e2dc in memblock_alloc_try_nid (size=108, align=<optimized
out>, min_addr=0, max_addr=0, nid=-1) at mm/memblock.c:1602
#2 0xc060f0b4 in memblock_alloc (size=<optimized out>,
align=<optimized out>) at ./include/linux/memblock.h:409
#3 cma_init_reserved_mem (base=1543503872, size=67108864,
order_per_bit=0, name=0xc04b9240 "reserved", res_cma=0xc07ccbdc
<dma_contiguous_default_area>) at mm/cma.c:190
#4 0xc060f2c0 in cma_declare_contiguous_nid (base=1543503872,
size=67108864, limit=1610612736, alignment=8388608, order_per_bit=0,
fixed=false, name=0xc04b9240 "reserved",
res_cma=0xc07ccbdc <dma_contiguous_default_area>, nid=-1) at mm/cma.c:352
#5 0xc0608cb6 in cma_declare_contiguous (alignment=<optimized out>,
order_per_bit=<optimized out>, name=<optimized out>,
res_cma=<optimized out>, fixed=<optimized out>,
limit=<optimized out>, size=<optimized out>, base=<optimized out>)
at ./include/linux/cma.h:28
#6 dma_contiguous_reserve_area (size=<optimized out>, base=<optimized
out>, limit=<optimized out>, res_cma=0xc07ccbdc
<dma_contiguous_default_area>, fixed=false)
at kernel/dma/contiguous.c:201
#7 0xc0608d22 in dma_contiguous_reserve (limit=<optimized out>) at
kernel/dma/contiguous.c:171
#8 0xc0604584 in arm_memblock_init (mdesc=0xc061bfe8
<__mach_desc_GENERIC_DT.35641>) at arch/arm/mm/init.c:230
#9 0xc060302c in setup_arch (cmdline_p=<optimized out>) at
arch/arm/kernel/setup.c:1132
#10 0xc06007d2 in start_kernel () at init/main.c:857
Using `si` in gdb, it looks like we maybe hit an exception vector?
x 1202 .section .vectors, "ax", %progbits
x
x 1203 .L__vectors_start:
x
x 1204 W(b) vector_rst
x
x 1205 W(b) vector_und
x
x 1206 W(ldr) pc, .L__vectors_start + 0x1000
x
x >1207 W(b) vector_pabt
Is the last thing I see, then `si` stops working. Not sure if `pabt`
is a recognizable acronym to anyone more familiar with ARM?
Happens regardless of your series, FWIW.
--
Thanks,
~Nick Desaulniers
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