2020-07-04 08:53:26

by Ignat Korchagin

Subject: [PATCH v2 1/3] um/kconfig: introduce CC_CAN_LINK_STATIC_NO_RUNTIME_DEPS

For statically linked UML build it is important to take into account the
standard C-library implementation. Some implementations, notably glibc have
caveats: even when linked statically, the final program might require some
runtime dependencies, if certain functions are used within the code.

Consider the following program:
int main(void)
{
getpwent();
return 0;
}

Compiling this program and linking statically with glibc produces the following
warning from the linker:
/usr/sbin/ld: /tmp/ccuthw1o.o: in function `main':
test.c:(.text+0x5): warning: Using 'getpwent' in statically linked
applications requires at runtime the shared libraries from the glibc version
used for linking

We will use the flag to detect such C-library implementation build time and
possibly disable static linking for UML to avoid producing a binary with
unexpected behaviour and dependencies.

Signed-off-by: Ignat Korchagin <[email protected]>
---
init/Kconfig | 6 ++++++
scripts/cc-can-link.sh | 5 +++--
2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index a46aa8f3174d..717a3ada765e 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -57,6 +57,12 @@ config CC_CAN_LINK_STATIC
default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) -static $(m64-flag)) if 64BIT
default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) -static $(m32-flag))

+config CC_CAN_LINK_STATIC_NO_RUNTIME_DEPS
+ bool
+ depends on UML && CC_CAN_LINK_STATIC
+ default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) -static -Xlinker --fatal-warnings $(m64-flag)) if 64BIT
+ default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) -static -Xlinker --fatal-warnings $(m32-flag))
+
config CC_HAS_ASM_GOTO
def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))

diff --git a/scripts/cc-can-link.sh b/scripts/cc-can-link.sh
index 6efcead31989..e5011a46103e 100755
--- a/scripts/cc-can-link.sh
+++ b/scripts/cc-can-link.sh
@@ -2,10 +2,11 @@
# SPDX-License-Identifier: GPL-2.0

cat << "END" | $@ -x c - -o /dev/null >/dev/null 2>&1
-#include <stdio.h>
+#include <sys/types.h>
+#include <pwd.h>
int main(void)
{
- printf("");
+ getpwent();
return 0;
}
END
--
2.20.1

2020-07-15 09:12:35

by Brendan Higgins

Subject: Re: [PATCH v2 1/3] um/kconfig: introduce CC_CAN_LINK_STATIC_NO_RUNTIME_DEPS

On Sat, Jul 4, 2020 at 1:52 AM Ignat Korchagin <[email protected]> wrote:
>
> For statically linked UML build it is important to take into account the
> standard C-library implementation. Some implementations, notably glibc have
> caveats: even when linked statically, the final program might require some
> runtime dependencies, if certain functions are used within the code.
>
> Consider the following program:
> int main(void)
> {
> getpwent();
> return 0;
> }
>
> Compiling this program and linking statically with glibc produces the following
> warning from the linker:
> /usr/sbin/ld: /tmp/ccuthw1o.o: in function `main':
> test.c:(.text+0x5): warning: Using 'getpwent' in statically linked
> applications requires at runtime the shared libraries from the glibc version
> used for linking
>
> We will use the flag to detect such C-library implementation build time and
> possibly disable static linking for UML to avoid producing a binary with
> unexpected behaviour and dependencies.
>
> Signed-off-by: Ignat Korchagin <[email protected]>

Nice.

Reviewed-by: Brendan Higgins <[email protected]>