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From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Alexandre Ghiti <alex@ghiti.fr>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Sasha Levin <sashal@kernel.org>,
	linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org,
	bpf@vger.kernel.org
Subject: [PATCH AUTOSEL 5.4 430/459] powerpc: Do not consider weak unresolved symbol relocations as bad
Date: Fri, 14 Feb 2020 11:01:20 -0500
Message-ID: <20200214160149.11681-430-sashal@kernel.org> (raw)
In-Reply-To: <20200214160149.11681-1-sashal@kernel.org>

From: Alexandre Ghiti <alex@ghiti.fr>

[ Upstream commit 43e76cd368fbb67e767da5363ffeaa3989993c8c ]

Commit 8580ac9404f6 ("bpf: Process in-kernel BTF") introduced two weak
symbols that may be unresolved at link time which result in an absolute
relocation to 0. relocs_check.sh emits the following warning:

"WARNING: 2 bad relocations
c000000001a41478 R_PPC64_ADDR64    _binary__btf_vmlinux_bin_start
c000000001a41480 R_PPC64_ADDR64    _binary__btf_vmlinux_bin_end"

whereas those relocations are legitimate even for a relocatable kernel
compiled with -pie option.

relocs_check.sh already excluded some weak unresolved symbols explicitly:
remove those hardcoded symbols and add some logic that parses the symbols
using nm, retrieves all the weak unresolved symbols and excludes those from
the list of the potential bad relocations.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200118170335.21440-1-alex@ghiti.fr
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/powerpc/Makefile.postlink     |  4 ++--
 arch/powerpc/tools/relocs_check.sh | 20 ++++++++++++--------
 2 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/Makefile.postlink b/arch/powerpc/Makefile.postlink
index 134f12f89b92b..2268396ff4bba 100644
--- a/arch/powerpc/Makefile.postlink
+++ b/arch/powerpc/Makefile.postlink
@@ -17,11 +17,11 @@ quiet_cmd_head_check = CHKHEAD $@
 quiet_cmd_relocs_check = CHKREL  $@
 ifdef CONFIG_PPC_BOOK3S_64
       cmd_relocs_check =						\
-	$(CONFIG_SHELL) $(srctree)/arch/powerpc/tools/relocs_check.sh "$(OBJDUMP)" "$@" ; \
+	$(CONFIG_SHELL) $(srctree)/arch/powerpc/tools/relocs_check.sh "$(OBJDUMP)" "$(NM)" "$@" ; \
 	$(BASH) $(srctree)/arch/powerpc/tools/unrel_branch_check.sh "$(OBJDUMP)" "$@"
 else
       cmd_relocs_check =						\
-	$(CONFIG_SHELL) $(srctree)/arch/powerpc/tools/relocs_check.sh "$(OBJDUMP)" "$@"
+	$(CONFIG_SHELL) $(srctree)/arch/powerpc/tools/relocs_check.sh "$(OBJDUMP)" "$(NM)" "$@"
 endif
 
 # `@true` prevents complaint when there is nothing to be done
diff --git a/arch/powerpc/tools/relocs_check.sh b/arch/powerpc/tools/relocs_check.sh
index 7b9fe0a567cf3..014e00e74d2b6 100755
--- a/arch/powerpc/tools/relocs_check.sh
+++ b/arch/powerpc/tools/relocs_check.sh
@@ -10,14 +10,21 @@
 # based on relocs_check.pl
 # Copyright © 2009 IBM Corporation
 
-if [ $# -lt 2 ]; then
-	echo "$0 [path to objdump] [path to vmlinux]" 1>&2
+if [ $# -lt 3 ]; then
+	echo "$0 [path to objdump] [path to nm] [path to vmlinux]" 1>&2
 	exit 1
 fi
 
-# Have Kbuild supply the path to objdump so we handle cross compilation.
+# Have Kbuild supply the path to objdump and nm so we handle cross compilation.
 objdump="$1"
-vmlinux="$2"
+nm="$2"
+vmlinux="$3"
+
+# Remove from the bad relocations those that match an undefined weak symbol
+# which will result in an absolute relocation to 0.
+# Weak unresolved symbols are of that form in nm output:
+# "                  w _binary__btf_vmlinux_bin_end"
+undef_weak_symbols=$($nm "$vmlinux" | awk '$1 ~ /w/ { print $2 }')
 
 bad_relocs=$(
 $objdump -R "$vmlinux" |
@@ -26,8 +33,6 @@ $objdump -R "$vmlinux" |
 	# These relocations are okay
 	# On PPC64:
 	#	R_PPC64_RELATIVE, R_PPC64_NONE
-	#	R_PPC64_ADDR64 mach_<name>
-	#	R_PPC64_ADDR64 __crc_<name>
 	# On PPC:
 	#	R_PPC_RELATIVE, R_PPC_ADDR16_HI,
 	#	R_PPC_ADDR16_HA,R_PPC_ADDR16_LO,
@@ -39,8 +44,7 @@ R_PPC_ADDR16_HI
 R_PPC_ADDR16_HA
 R_PPC_RELATIVE
 R_PPC_NONE' |
-	grep -E -v '\<R_PPC64_ADDR64[[:space:]]+mach_' |
-	grep -E -v '\<R_PPC64_ADDR64[[:space:]]+__crc_'
+	([ "$undef_weak_symbols" ] && grep -F -w -v "$undef_weak_symbols" || cat)
 )
 
 if [ -z "$bad_relocs" ]; then
-- 
2.20.1


  parent reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200214160149.11681-1-sashal@kernel.org>
2020-02-14 15:56 ` [PATCH AUTOSEL 5.4 114/459] bpftool: Don't crash on missing xlated program instructions Sasha Levin
2020-02-14 15:56 ` [PATCH AUTOSEL 5.4 115/459] bpf, sockhash: Synchronize_rcu before free'ing map Sasha Levin
2020-02-14 15:56 ` [PATCH AUTOSEL 5.4 116/459] bpf, sockmap: Check update requirements after locking Sasha Levin
2020-02-14 15:56 ` [PATCH AUTOSEL 5.4 117/459] bpf: Improve bucket_log calculation logic Sasha Levin
2020-02-14 15:56 ` [PATCH AUTOSEL 5.4 118/459] bpf, sockmap: Don't sleep while holding RCU lock on tear-down Sasha Levin
2020-02-14 15:57 ` [PATCH AUTOSEL 5.4 186/459] samples/bpf: Set -fno-stack-protector when building BPF programs Sasha Levin
2020-02-14 15:57 ` [PATCH AUTOSEL 5.4 227/459] bpf: Print error message for bpftool cgroup show Sasha Levin
2020-02-14 15:58 ` [PATCH AUTOSEL 5.4 248/459] tools lib api fs: Fix gcc9 stringop-truncation compilation error Sasha Levin
2020-02-14 15:59 ` [PATCH AUTOSEL 5.4 307/459] bpf: Return -EBADRQC for invalid map type in __bpf_tx_xdp_map Sasha Levin
2020-02-14 16:00 ` [PATCH AUTOSEL 5.4 376/459] bpf, btf: Always output invariant hit in pahole DWARF to BTF transform Sasha Levin
2020-02-14 16:00 ` [PATCH AUTOSEL 5.4 397/459] selftests: bpf: Reset global state between reuseport test runs Sasha Levin
2020-02-14 16:01 ` [PATCH AUTOSEL 5.4 415/459] bpf: map_seq_next should always increase position index Sasha Levin
2020-02-14 16:01 ` Sasha Levin [this message]
2020-02-14 16:01 ` [PATCH AUTOSEL 5.4 455/459] i40e: Relax i40e_xsk_wakeup's return value when PF is busy Sasha Levin

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