[v3,16/27] compiler: Option to add PROVIDE_HIDDEN replacement for weak symbols
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Message ID 20180523195421.180248-17-thgarnie@google.com
State New
Headers show

Commit Message

Thomas Garnier May 23, 2018, 7:54 p.m. UTC
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 <thgarnie@google.com>
---
 init/Kconfig            |  7 +++++++
 scripts/link-vmlinux.sh | 14 ++++++++++++++
 2 files changed, 21 insertions(+)

Comments

Randy Dunlap May 23, 2018, 9:16 p.m. UTC | #1
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 <thgarnie@google.com>
> ---
>  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).

	                                        PIE                    PIE).

> +

Patch
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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