[PATCH AUTOSEL 5.4 28/40] recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64.

From: Sasha Levin
Date: Sat Aug 08 2020 - 19:39:43 EST

From: Gregory Herrero <gregory.herrero@xxxxxxxxxx>

[ Upstream commit ea0eada45632f4807b2f49de951072283e2d781c ]

Currently, if a section has a relocation to '_mcount' symbol, a new
__mcount_loc entry will be added whatever the relocation type is.
This is problematic when a relocation to '_mcount' is in the middle of a
section and is not a call for ftrace use.

Such relocation could be generated with below code for example:
bool is_mcount(unsigned long addr)
return (target == (unsigned long) &_mcount);

With this snippet of code, ftrace will try to patch the mcount location
generated by this code on module load and fail with:

Call trace:
---[ end trace d828d06b36ad9d59 ]---
ftrace failed to modify
[<ffffa2dbf3a3a41c>] 0xffffa2dbf3a3a41c
actual: 66:a9:3c:90
Initializing ftrace call sites
ftrace record flags: 2000000
expected tramp: ffffa2dc6cf66724

So Limit the relocation type to R_AARCH64_CALL26 as in perl version of

Fixes: af64d2aa872a ("ftrace: Add arm64 support to recordmcount")
Signed-off-by: Gregory Herrero <gregory.herrero@xxxxxxxxxx>
Acked-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20200717143338.19302-1-gregory.herrero@xxxxxxxxxx
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
scripts/recordmcount.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
index 7225107a9aafe..e59022b3f1254 100644
--- a/scripts/recordmcount.c
+++ b/scripts/recordmcount.c
@@ -434,6 +434,11 @@ static int arm_is_fake_mcount(Elf32_Rel const *rp)
return 1;

+static int arm64_is_fake_mcount(Elf64_Rel const *rp)
+ return ELF64_R_TYPE(w(rp->r_info)) != R_AARCH64_CALL26;
/* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
* http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
* We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
@@ -547,6 +552,7 @@ static int do_file(char const *const fname)
make_nop = make_nop_arm64;
rel_type_nop = R_AARCH64_NONE;
ideal_nop = ideal_nop4_arm64;
+ is_fake_mcount64 = arm64_is_fake_mcount;
case EM_IA_64: reltype = R_IA64_IMM64; break;
case EM_MIPS: /* reltype: e_class */ break;