Scenario 1, ARMv7: ==================

If code in arch/arm/kernel/ftrace.c would operate on mcount() pointer the following may be generated:

00000230 <prealloc_fixed_plts>: 230: b5f8 push {r3, r4, r5, r6, r7, lr} 232: b500 push {lr} 234: f7ff fffe bl 0 <__gnu_mcount_nc> 234: R_ARM_THM_CALL __gnu_mcount_nc 238: f240 0600 movw r6, #0 238: R_ARM_THM_MOVW_ABS_NC __gnu_mcount_nc 23c: f8d0 1180 ldr.w r1, [r0, #384] ; 0x180

FTRACE currently is not able to deal with it:

WARNING: CPU: 0 PID: 0 at .../kernel/trace/ftrace.c:1979 ftrace_bug+0x1ad/0x230() ... CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.116-... #1 ... [<c0314e3d>] (unwind_backtrace) from [<c03115e9>] (show_stack+0x11/0x14) [<c03115e9>] (show_stack) from [<c051a7f1>] (dump_stack+0x81/0xa8) [<c051a7f1>] (dump_stack) from [<c0321c5d>] (warn_slowpath_common+0x69/0x90) [<c0321c5d>] (warn_slowpath_common) from [<c0321cf3>] (warn_slowpath_null+0x17/0x1c) [<c0321cf3>] (warn_slowpath_null) from [<c038ee9d>] (ftrace_bug+0x1ad/0x230) [<c038ee9d>] (ftrace_bug) from [<c038f1f9>] (ftrace_process_locs+0x27d/0x444) [<c038f1f9>] (ftrace_process_locs) from [<c08915bd>] (ftrace_init+0x91/0xe8) [<c08915bd>] (ftrace_init) from [<c0885a67>] (start_kernel+0x34b/0x358) [<c0885a67>] (start_kernel) from [<00308095>] (0x308095) ---[ end trace cb88537fdc8fa200 ]--- ftrace failed to modify [<c031266c>] prealloc_fixed_plts+0x8/0x60 actual: 44:f2:e1:36 ftrace record flags: 0 (0) expected tramp: c03143e9

Scenario 2, ARMv4T: ===================

ftrace: allocating 14435 entries in 43 pages ------------[ cut here ]------------ WARNING: CPU: 0 PID: 0 at kernel/trace/ftrace.c:2029 ftrace_bug+0x204/0x310 CPU: 0 PID: 0 Comm: swapper Not tainted 4.19.5 #1 Hardware name: Cirrus Logic EDB9302 Evaluation Board [<c0010a24>] (unwind_backtrace) from [<c000ecb0>] (show_stack+0x20/0x2c) [<c000ecb0>] (show_stack) from [<c03c72e8>] (dump_stack+0x20/0x30) [<c03c72e8>] (dump_stack) from [<c0021c18>] (__warn+0xdc/0x104) [<c0021c18>] (__warn) from [<c0021d7c>] (warn_slowpath_null+0x4c/0x5c) [<c0021d7c>] (warn_slowpath_null) from [<c0095360>] (ftrace_bug+0x204/0x310) [<c0095360>] (ftrace_bug) from [<c04dabac>] (ftrace_init+0x3b4/0x4d4) [<c04dabac>] (ftrace_init) from [<c04cef4c>] (start_kernel+0x20c/0x410) [<c04cef4c>] (start_kernel) from [<00000000>] ( (null)) ---[ end trace 0506a2f5dae6b341 ]--- ftrace failed to modify [<c000c350>] perf_trace_sys_exit+0x5c/0xe8 actual: 1e:ff:2f:e1 Initializing ftrace call sites ftrace record flags: 0 (0) expected tramp: c000fb24

The analysis for this problem has been already performed previously, refer to the link below.

Fix the above problems by allowing only selected reloc types in __mcount_loc. The list itself comes from the legacy recordmcount.pl script.

Cc: stable@vger.kernel.org Link: https://lore.kernel.org/lkml/56961010.6000806@pengutronix.de/ Fixes: ed60453fa8 ("ARM: 6511/1: ftrace: add ARM support for C version of recordmcount") Signed-off-by: Alexander Sverdlin alexander.sverdlin@nokia.com --- scripts/recordmcount.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)

diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c index 895c40e8679f..3b0dcf38fd8b 100644 --- a/scripts/recordmcount.c +++ b/scripts/recordmcount.c @@ -39,6 +39,10 @@ #define R_AARCH64_ABS64 257 #endif

+#define R_ARM_PC24 1 +#define R_ARM_THM_CALL 10 +#define R_ARM_CALL 28 + static int fd_map; /* File descriptor for file being modified. */ static int mmap_failed; /* Boolean flag. */ static char gpfx; /* prefix for global symbol name (sometimes '_') */ @@ -414,6 +418,18 @@ is_mcounted_section_name(char const *const txtname) #define RECORD_MCOUNT_64 #include "recordmcount.h"

+static int arm_is_fake_mcount(Elf32_Rel const *rp) +{ + switch (ELF32_R_TYPE(w(rp->r_info))) { + case R_ARM_THM_CALL: + case R_ARM_CALL: + case R_ARM_PC24: + return 0; + } + + return 1; +} + /* 64-bit EM_MIPS has weird ELF64_Rela.r_info. * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.p... * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40] @@ -515,6 +531,7 @@ do_file(char const *const fname) altmcount = "__gnu_mcount_nc"; make_nop = make_nop_arm; rel_type_nop = R_ARM_NONE; + is_fake_mcount32 = arm_is_fake_mcount; break; case EM_AARCH64: reltype = R_AARCH64_ABS64;