hi
consider this simple file "pippo.c" , that tests linking with the dts library
vvvvvvvvvvvvvvvvvvvv
extern int dts_init();
int main(){
dts_init();
}
^^^^^^^^^^^^^^^^^^^
here are some examples of compiling:
the following commands are fine:
$ gcc -Wl,--as-needed -o pippo pippo.c -ldts -lm
$ gcc -o pippo pippo.c -lm -ldts
$ gcc -o pippo pippo.c -ldts -lm
but this command fails:
$ gcc -Wl,--as-needed -o pippo pippo.c -lm -ldts
/usr/lib/gcc/x86_64-linux-gnu/4.1.2/../../../../lib64/libdts.a(parse.o): In
function `dts_init':
(.text+0xcf): undefined reference to `cos'
[...]
collect2: ld returned 1 exit status
My interpretation is:
when the linker sees '-lm', and sees that "pippo.c" is not calling anything in
it, it drops '-lm' ; then it reaches '-ldts' and links in dts_init() and finds
out that it needs sin() and cos() , and has no library to link to, and fails.
Here are two (mutually exclusive) requests:
1) you should explain this behavior in the docs;
for example, you may add in the man page,where the option --as-needed
is documented, a phrase as
"When using --as-needed , the order in which the libraries appear in the
command line is relevant: any library X
must precede all libraries Y that offer symbols that X uses."
2) [feature request] I request that also 'ld --as-needed' may
be accept the latter compilation. For example, 'ld --as-needed' may read
all libraries in command line and link them in order, properly
flagging those that are really needed ; at the end
of the process, it would then go again trough the list and only add
DT_NEEDED for those that are flagged.
thanks
a.
--
Summary: --as-needed and order of libraries in linking
Product: binutils
Version: 2.17
Status: NEW
Severity: minor
Priority: P2
Component: ld
AssignedTo: unassigned at sources dot redhat dot com
ReportedBy: mennucc1 at debian dot org
CC: bug-binutils at gnu dot org
GCC build triplet: x86_64-linux-gnu
GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu
http://sourceware.org/bugzilla/show_bug.cgi?id=3612
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