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[PATCH] allow empty string as argument to -Map

Rasmus Villemoes rv@rasmusvillemoes.dk
Tue May 26 07:01:40 GMT 2020 
In meta-build systems like Yocto, it's rather easy to add flags like
-fdata-sections, -ffunction-sections, -Wl,--gc-sections to global
CFLAGS/LDFLAGS. But when digging into what effect those had on the
build of a particular package, it would be nice to also have a map
file automatically generated. That's currently a bit harder, since it
requires patching the build system of each individual package to add
something like -Wl,-Map=$@.map somewhere.

My first instinct was to make the argument to -Map optional, but that
will of course break anybody that uses the form "-Map foo.map" rather
than "-Map=foo.map".

So, as the next best thing, use a previously bogus value (the empty
string) as a sentinel to indicate "use the output filename + .map".

Signed-off-by: Rasmus Villemoes <rv@rasmusvillemoes.dk>
---
 ld/ld.texi  | 4 +++-
 ld/lexsup.c | 5 +++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/ld/ld.texi b/ld/ld.texi
index 9f562935be..25ce1d6524 100644
--- a/ld/ld.texi
+++ b/ld/ld.texi
@@ -1759,7 +1759,9 @@ Print a summary of all target-specific options on the standard output and exit.
 @kindex -Map=@var{mapfile}
 @item -Map=@var{mapfile}
 Print a link map to the file @var{mapfile}.  See the description of the
-@option{-M} option, above.
+@option{-M} option, above. Specifying the empty string as @var{mapfile}
+(that is, @code{-Map=}) causes the link map to be written to a file
+named after the @var{output} file, with @code{.map} appended.
 
 @cindex memory usage
 @kindex --no-keep-memory
diff --git a/ld/lexsup.c b/ld/lexsup.c
index 2597e2d630..e7ab07b50f 100644
--- a/ld/lexsup.c
+++ b/ld/lexsup.c
@@ -1617,6 +1617,11 @@ parse_args (unsigned argc, char **argv)
 	}
     }
 
+  if (config.map_filename && !config.map_filename[0]) {
+    if (asprintf (&config.map_filename, "%s.map", output_filename) < 0)
+      einfo (_("%F%P: %s: can not create name of map file: %E\n"));
+  }
+
   if (command_line.soname && command_line.soname[0] == '\0')
     {
       einfo (_("%P: SONAME must not be empty string; ignored\n"));
-- 
2.23.0
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