Re: [PATCH v3 16/27] compiler: Option to add PROVIDE_HIDDEN replacement for weak symbols

[Randy Dunlap]

On 05/23/2018 12:54 PM, Thomas Garnier wrote:
> Provide an option to have a PROVIDE_HIDDEN (linker script) entry for
> each weak symbol. This option solve an error in x86_64 where the linker

solves

> optimizes pie generate code to be non-pie because --emit-relocs was used

generated

> instead of -pie (to reduce dynamic relocations).
> 
> Signed-off-by: Thomas Garnier 
> ---
>  init/Kconfig|  7 +++
>  scripts/link-vmlinux.sh | 14 ++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index 0fc3a58d9f2f..2866cca86b4a 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1954,6 +1954,13 @@ config ASN1
> inform it as to what tags are to be expected in a stream and what
> functions to call on what tags.
>  
> +config WEAK_PROVIDE_HIDDEN
> + bool
> + help
> +   Generate linker script PROVIDE_HIDDEN entries for all weak symbols. It
> +   allows to prevent non-pie code being replaced by the linker if the

non-PIE

> +   emit-relocs option is used instead of pie (useful for x86_64 pie).

PIEPIE).

> +


-- 
~Randy
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[PATCH v3 16/27] compiler: Option to add PROVIDE_HIDDEN replacement for weak symbols

[Thomas Garnier via Virtualization]

Provide an option to have a PROVIDE_HIDDEN (linker script) entry for
each weak symbol. This option solve an error in x86_64 where the linker
optimizes pie generate code to be non-pie because --emit-relocs was used
instead of -pie (to reduce dynamic relocations).

Signed-off-by: Thomas Garnier 
---
 init/Kconfig|  7 +++
 scripts/link-vmlinux.sh | 14 ++
 2 files changed, 21 insertions(+)

diff --git a/init/Kconfig b/init/Kconfig
index 0fc3a58d9f2f..2866cca86b4a 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1954,6 +1954,13 @@ config ASN1
  inform it as to what tags are to be expected in a stream and what
  functions to call on what tags.
 
+config WEAK_PROVIDE_HIDDEN
+   bool
+   help
+ Generate linker script PROVIDE_HIDDEN entries for all weak symbols. It
+ allows to prevent non-pie code being replaced by the linker if the
+ emit-relocs option is used instead of pie (useful for x86_64 pie).
+
 source "kernel/Kconfig.locks"
 
 config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 4bf811c09f59..f5d31119b9d7 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -142,6 +142,17 @@ kallsyms()
${CC} ${aflags} -c -o ${2} ${afile}
 }
 
+gen_weak_provide_hidden()
+{
+if [ -n "${CONFIG_WEAK_PROVIDE_HIDDEN}" ]; then
+local pattern="s/^\s\+ w \(\w\+\)$/PROVIDE_HIDDEN(\1 = .);/gp"
+echo -e "SECTIONS {\n. = _end;" > .tmp_vmlinux_hiddenld
+${NM} ${1} | sed -n "${pattern}" >> .tmp_vmlinux_hiddenld
+echo "}" >> .tmp_vmlinux_hiddenld
+LDFLAGS_vmlinux="${LDFLAGS_vmlinux} -T .tmp_vmlinux_hiddenld"
+fi
+}
+
 # Create map file with all symbols from ${1}
 # See mksymap for additional details
 mksysmap()
@@ -226,6 +237,9 @@ modpost_link vmlinux.o
 # modpost vmlinux.o to check for section mismatches
 ${MAKE} -f "${srctree}/scripts/Makefile.modpost" vmlinux.o
 
+# Generate weak linker script
+gen_weak_provide_hidden vmlinux.o
+
 kallsymso=""
 kallsyms_vmlinux=""
 if [ -n "${CONFIG_KALLSYMS}" ]; then
-- 
2.17.0.441.gb46fe60e1d-goog

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