With ppc64 -mprofile-kernel and ppc32 -pg, profiling instructions to
call into ftrace are emitted right at function entry. The instruction
sequence used is minimal to reduce overhead. Crucially, a stackframe is
not created for the function being traced. This breaks stack unwinding
since the function being traced does not have a stackframe for itself.
As such, it never shows up in the backtrace:
/sys/kernel/debug/tracing # echo 1 > /proc/sys/kernel/stack_tracer_enabled
/sys/kernel/debug/tracing # cat stack_trace
Depth Size Location (17 entries)
----- ---- --------
0) 4144 32 ftrace_call+0x4/0x44
1) 4112 432 get_page_from_freelist+0x26c/0x1ad0
2) 3680 496 __alloc_pages+0x290/0x1280
3) 3184 336 __folio_alloc+0x34/0x90
4) 2848 176 vma_alloc_folio+0xd8/0x540
5) 2672 272 __handle_mm_fault+0x700/0x1cc0
6) 2400 208 handle_mm_fault+0xf0/0x3f0
7) 2192 80 ___do_page_fault+0x3e4/0xbe0
8) 2112 160 do_page_fault+0x30/0xc0
9) 1952 256 data_access_common_virt+0x210/0x220
10) 1696 400 0xc00000000f16b100
11) 1296 384 load_elf_binary+0x804/0x1b80
12) 912 208 bprm_execve+0x2d8/0x7e0
13) 704 64 do_execveat_common+0x1d0/0x2f0
14) 640 160 sys_execve+0x54/0x70
15) 480 64 system_call_exception+0x138/0x350
16) 416 416 system_call_common+0x160/0x2c4
Fix this by having ftrace create a dummy stackframe for the function
being traced. With this, backtraces now capture the function being
traced:
/sys/kernel/debug/tracing # cat stack_trace
Depth Size Location (17 entries)
----- ---- --------
0) 3888 32 _raw_spin_trylock+0x8/0x70
1) 3856 576 get_page_from_freelist+0x26c/0x1ad0
2) 3280 64 __alloc_pages+0x290/0x1280
3) 3216 336 __folio_alloc+0x34/0x90
4) 2880 176 vma_alloc_folio+0xd8/0x540
5) 2704 416 __handle_mm_fault+0x700/0x1cc0
6) 2288 96 handle_mm_fault+0xf0/0x3f0
7) 2192 48 ___do_page_fault+0x3e4/0xbe0
8) 2144 192 do_page_fault+0x30/0xc0
9) 1952 608 data_access_common_virt+0x210/0x220
10) 1344 16 0xc0000000334bbb50
11) 1328 416 load_elf_binary+0x804/0x1b80
12) 912 64 bprm_execve+0x2d8/0x7e0
13) 848 176 do_execveat_common+0x1d0/0x2f0
14) 672 192 sys_execve+0x54/0x70
15) 480 64 system_call_exception+0x138/0x350
16) 416 416 system_call_common+0x160/0x2c4
This results in two additional stores in the ftrace entry code, but
produces reliable backtraces.
Fixes: 153086644f ("powerpc/ftrace: Add support for -mprofile-kernel ftrace ABI")
Cc: stable@vger.kernel.org
Signed-off-by: Naveen N Rao <naveen@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230621051349.759567-1-naveen@kernel.org
PC-Relative or PCREL addressing is an extension to the ELF ABI which
uses Power ISA v3.1 PC-relative instructions to calculate addresses,
rather than the traditional TOC scheme.
Add an option to build vmlinux using pcrel addressing. Modules continue
to use TOC addressing.
- TOC address helpers and r2 are poisoned with -1 when running vmlinux.
r2 could be used for something useful once things are ironed out.
- Assembly must call C functions with @notoc annotation, or the linker
complains aobut a missing nop after the call. This is done with the
CFUNC macro introduced earlier.
- Boot: with the exception of prom_init, the execution branches to the
kernel virtual address early in boot, before any addresses are
generated, which ensures 34-bit pcrel addressing does not miss the
high PAGE_OFFSET bits. TOC relative addressing has a similar
requirement. prom_init does not go to the virtual address and its
addresses should not carry over to the post-prom kernel.
- Ftrace trampolines are converted from TOC addressing to pcrel
addressing, including module ftrace trampolines that currently use the
kernel TOC to find ftrace target functions.
- BPF function prologue and function calling generation are converted
from TOC to pcrel.
- copypage_64.S has an interesting problem, prefixed instructions have
alignment restrictions so the linker can add padding, which makes the
assembler treat the difference between two local labels as
non-constant even if alignment is arranged so padding is not required.
This may need toolchain help to solve nicely, for now move the prefix
instruction out of the alternate patch section to work around it.
This reduces kernel text size by about 6%.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230408021752.862660-6-npiggin@gmail.com
Add an option to build kernel and module with prefixed instructions if
the CPU and toolchain support it.
This is not related to kernel support for userspace execution of
prefixed instructions.
Building with prefixed instructions breaks some extended inline asm
memory addressing, for example it will provide immediates that exceed
the range of simple load/store displacement. Whether this is a
toolchain or a kernel asm problem remains to be seen. For now, these
are replaced with simpler and less efficient direct register addressing
when compiling with prefixed.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230408021752.862660-4-npiggin@gmail.com
This is a common offset that currently uses the overloaded
STACK_FRAME_OVERHEAD constant. It's easier to read and more
flexible to use a specific regs offset for this.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221127124942.1665522-8-npiggin@gmail.com
A later change stops the kernel using r2 and loads it with a poison
value. Provide a PACATOC loading abstraction which can hide this
detail.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220926034057.2360083-5-npiggin@gmail.com
Use helper macros to access global variables, and place them in .data
sections rather than in .toc. Putting addresses in TOC is not required
because the kernel is linked with a single TOC.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220926034057.2360083-3-npiggin@gmail.com
Since commit 87c78b612f ("powerpc: Fix all occurences of "the the"")
fixed "the the", there's now a steady stream of patches fixing other
duplicate words.
Just fix them all at once, to save the overhead of dealing with
individual patches for each case.
This leaves a few cases of "that that", which in some contexts is
correct.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220718095158.326606-1-mpe@ellerman.id.au
The ppc_inst_as_str() macro tries to make printing variable length,
aka "prefixed", instructions convenient. It mostly succeeds, but it does
hide an on-stack buffer, which triggers stack protector.
More problematically it doesn't compile at all with GCC 12,
with -Wdangling-pointer, due to the fact that it returns the char buffer
declared inside the macro:
arch/powerpc/kernel/trace/ftrace.c: In function '__ftrace_modify_call':
./include/linux/printk.h:475:44: error: using a dangling pointer to '__str' [-Werror=dangling-pointer=]
475 | #define printk(fmt, ...) printk_index_wrap(_printk, fmt, ##__VA_ARGS__)
...
arch/powerpc/kernel/trace/ftrace.c:567:17: note: in expansion of macro 'pr_err'
567 | pr_err("Not expected bl: opcode is %s\n", ppc_inst_as_str(op));
| ^~~~~~
./arch/powerpc/include/asm/inst.h:156:14: note: '__str' declared here
156 | char __str[PPC_INST_STR_LEN]; \
| ^~~~~
This could be fixed by having the caller declare the buffer, but in some
places there'd need to be two buffers. In all cases where
ppc_inst_as_str() is used the output is not really meant for user
consumption, it's almost always indicative of a kernel bug.
A simpler solution is to just print the value as an unsigned long. For
normal instructions the output is identical. For prefixed instructions
the value is printed as a single 64-bit quantity, whereas previously the
low half was printed first. But that is good enough for debug output,
especially as prefixed instructions will be rare in kernel code in
practice.
Old:
c000000000111170 60420000 ori r2,r2,0
c000000000111174 04100001 e580fb00 .long 0xe580fb0004100001
New:
c00000000010f90c 60420000 ori r2,r2,0
c00000000010f910 e580fb0004100001 .long 0xe580fb0004100001
Reported-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reported-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Tested-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://lore.kernel.org/r/20220531065936.3674348-1-mpe@ellerman.id.au
Since commit 0c0c52306f ("powerpc: Only support DYNAMIC_FTRACE not
static"), CONFIG_DYNAMIC_FTRACE is always selected when
CONFIG_FUNCTION_TRACER is selected.
To avoid confusion and have the reader wonder what's happen when
CONFIG_FUNCTION_TRACER is selected and CONFIG_DYNAMIC_FTRACE is not,
use CONFIG_FUNCTION_TRACER in ifdefs instead of CONFIG_DYNAMIC_FTRACE.
As CONFIG_FUNCTION_GRAPH_TRACER depends on CONFIG_FUNCTION_TRACER,
ftrace.o doesn't need to appear for both symbols in Makefile.
Then as ftrace.o is built only when CONFIG_FUNCTION_TRACER is selected
ifdef CONFIG_FUNCTION_TRACER is not needed in ftrace.c, and since it
implies CONFIG_DYNAMIC_FTRACE, CONFIG_DYNAMIC_FTRACE is not needed
in ftrace.c
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/628d357503eb90b4a034f99b7df516caaff4d279.1652074503.git.christophe.leroy@csgroup.eu
Inlining ftrace_modify_code(), it increases a bit the
size of ftrace code but brings 5% improvment on ftrace
activation.
Usually in C files we let gcc decide what to do but here
it really help to 'help' gcc to decide to inline, thought
we don't want to force it with an __always_inline that
would be too much for CONFIG_CC_OPTIMIZE_FOR_SIZE.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1597a06d57cfc80e6853838c4066e799bf6c7977.1652074503.git.christophe.leroy@csgroup.eu
Since commit d5937db114 ("powerpc/code-patching: Fix patch_branch()
return on out-of-range failure") patch_branch() fails with -ERANGE
when trying to branch out of range.
No need to perform the test twice. Remove redundant create_branch()
calls.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/aa45fbad0b4b7493080835d8276c0cb4ce146503.1652074503.git.christophe.leroy@csgroup.eu
When we have CONFIG_DYNAMIC_FTRACE_WITH_ARGS,
prepare_ftrace_return() is called by ftrace_graph_func()
otherwise prepare_ftrace_return() is called from assembly.
Refactor prepare_ftrace_return() into a static
__prepare_ftrace_return() that will be called by both
prepare_ftrace_return() and ftrace_graph_func().
It will allow GCC to fold __prepare_ftrace_return() inside
ftrace_graph_func().
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/0d42deafe353980c66cf19d3132638c05ba9f4a9.1652074503.git.christophe.leroy@csgroup.eu
We originally added asm-prototypes.h in commit 42f5b4cacd ("powerpc:
Introduce asm-prototypes.h"). It's purpose was for prototypes of C
functions that are only called from asm, in order to fix sparse
warnings about missing prototypes.
A few months later Nick added a different use case in
commit 4efca4ed05 ("kbuild: modversions for EXPORT_SYMBOL() for asm")
for C prototypes for exported asm functions. This is basically the
inverse of our original usage.
Since then we've added various prototypes to asm-prototypes.h for both
reasons, meaning we now need to unstitch it all.
Dispatch prototypes of C functions into relevant headers and keep
only the prototypes for functions defined in assembly.
For the time being, leave prom_init() there because moving it
into asm/prom.h or asm/setup.h conflicts with
drivers/gpu/drm/nouveau/nvkm/subdev/bios/shadowrom.o
This will be fixed later by untaggling asm/pci.h and asm/prom.h
or by renaming the function in shadowrom.c
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/62d46904eca74042097acf4cb12c175e3067f3d1.1646413435.git.christophe.leroy@csgroup.eu
Add some line breaks to better match the file's style, add
some space after comma and fix a couple of misplaced blanks.
Suggested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/973506292d0c7b05c06530c8e11803ce38e5eda2.1644949750.git.christophe.leroy@csgroup.eu
When FL_SAVE_REGS is not set we get here via ftrace_caller()
which doesn't save all registers.
ftrace_caller() explicitely clears regs.msr, so we can rely
on it to know where we come from. We don't expect MSR register
to be 0 at all when involving ftrace.
Fixes: 40b035efe2 ("powerpc/ftrace: Implement CONFIG_DYNAMIC_FTRACE_WITH_ARGS")
Reported-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/2f9a7e898c93cc7438ef5ccd47cb9c3a9c5b53ef.1644949750.git.christophe.leroy@csgroup.eu
The function_graph_enter() does not provide any recursion protection.
Add a protection in prepare_ftrace_return() in case
function_graph_enter() calls something that gets
function graph traced.
Fixes: 830213786c ("powerpc/ftrace: directly call of function graph tracer by ftrace caller")
Reported-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/74edf2ff0a60e66b0d9225a137100a86a0557032.1644949750.git.christophe.leroy@csgroup.eu
Also save r1 in ftrace_caller()
r1 is needed during unwinding when the function_graph tracer
is active.
Fixes: 830213786c ("powerpc/ftrace: directly call of function graph tracer by ftrace caller")
Reported-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/ff535e86d3a69376a6d89168511d4e403835f18b.1644949750.git.christophe.leroy@csgroup.eu
Modify function graph tracer to be handled directly by the standard
ftrace caller.
This is made possible as powerpc now supports
CONFIG_DYNAMIC_FTRACE_WITH_ARGS.
This change simplifies the call of function graph ftrace.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/04d196585ff81bde06a000bd9c633a33a5b21130.1640017960.git.christophe.leroy@csgroup.eu
ftrace_enable_ftrace_graph_caller() and
ftrace_disable_ftrace_graph_caller() have common code.
They will have even more common code after following patch.
Refactor into a single ftrace_modify_ftrace_graph_caller() function.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/f37785a531f1a8f201e1b3da45997a5c77e9d820.1640017960.git.christophe.leroy@csgroup.eu
Introduce macros that operate on a (start, end) range of GPRs, which
reduces lines of code and need to do mental arithmetic while reading the
code.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Segher Boessenkool <segher@kernel.crashing.org>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211022061322.2671178-1-npiggin@gmail.com
Unlike PPC64, PPC32 doesn't require any special compiler option
to get _mcount() call not clobbering registers.
Provide ftrace_regs_caller() and ftrace_regs_call() and activate
HAVE_DYNAMIC_FTRACE_WITH_REGS.
That's heavily copied from ftrace_64_mprofile.S
For the time being leave livepatching aside, it will come with
following patch.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1862dc7719855cc2a4eec80920d94c955877557e.1635423081.git.christophe.leroy@csgroup.eu
All functions calling _mcount do it exactly the same way, with the
following sequence of instructions:
c07de788: 7c 08 02 a6 mflr r0
c07de78c: 90 01 00 04 stw r0,4(r1)
c07de790: 4b 84 13 65 bl c001faf4 <_mcount>
Allthough LR is pushed on stack, it is still in r0 while entering
_mcount().
Function arguments are in r3-r10, so r11 and r12 are still available
at that point.
Do like PPC64 and use r12 to move LR into CTR, so that r0 is preserved
and doesn't need to be restored from the stack.
While at it, bring back the EXPORT_SYMBOL at the end of _mcount.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/24a3ba7db388537c44a038026f926d885372e6d3.1635423081.git.christophe.leroy@csgroup.eu
'struct ppc_inst' is an internal representation of an instruction, but
in-memory instructions are and will remain a table of 'u32' forever.
Replace all 'struct ppc_inst *' used for locating an instruction in
memory by 'u32 *'. This removes a lot of undue casts to 'struct
ppc_inst *'.
It also helps locating ab-use of 'struct ppc_inst' dereference.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
[mpe: Fix ppc_inst_next(), use u32 instead of unsigned int]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/7062722b087228e42cbd896e39bfdf526d6a340a.1621516826.git.christophe.leroy@csgroup.eu
