[PATCH] D58326: [Driver][Gnu] Support -nolibc flag

[Roland McGrath via cfe-commits]

See
https://fuchsia.googlesource.com/fuchsia/+/48c987febf4077e52985f1ce1edc957b39bc5481/zircon/public/gn/config/BUILD.gn#219
and
https://fuchsia.googlesource.com/fuchsia/+/48c987febf4077e52985f1ce1edc957b39bc5481/zircon/public/gn/config/libc-dummy
for what happens without it...

On Sat, Feb 16, 2019 at 5:29 PM Eric Christopher <echristo at gmail.com> wrote:

> Weird. Ok.
>
> On Sat, Feb 16, 2019, 5:20 PM Petr Hosek via Phabricator <
> reviews at reviews.llvm.org> wrote:
>
>> phosek created this revision.
>> phosek added reviewers: echristo, mcgrathr.
>> Herald added a project: clang.
>> Herald added a subscriber: cfe-commits.
>>
>> This can be used to disable libc linking. This flag is supported by
>> GCC since version 9 as well as some Clang target toolchains.
>>
>>
>> Repository:
>>   rC Clang
>>
>> https://reviews.llvm.org/D58326
>>
>> Files:
>>   clang/lib/Driver/ToolChains/Gnu.cpp
>>   clang/test/Driver/nodefaultlib.c
>>   clang/test/Driver/nolibc.c
>>
>>
>> Index: clang/test/Driver/nolibc.c
>> ===================================================================
>> --- /dev/null
>> +++ clang/test/Driver/nolibc.c
>> @@ -0,0 +1,5 @@
>> +// RUN: %clang -target i686-pc-linux-gnu -### -rtlib=libgcc -nolibc %s
>> 2>&1 | FileCheck %s
>> +// CHECK: crtbegin
>> +// CHECK: "-lgcc"
>> +// CHECK-NOT: "-lc"
>> +// CHECK: crtend
>> Index: clang/test/Driver/nodefaultlib.c
>> ===================================================================
>> --- clang/test/Driver/nodefaultlib.c
>> +++ clang/test/Driver/nodefaultlib.c
>> @@ -1,4 +1,4 @@
>> -// RUN: %clang -target i686-pc-linux-gnu -### -nodefaultlibs %s 2>&1 |
>> FileCheck -check-prefix=TEST1 %s
>> +// RUN: %clang -target i686-pc-linux-gnu -### -rtlib=libgcc
>> -nodefaultlibs %s 2>&1 | FileCheck -check-prefix=TEST1 %s
>>  // TEST1-NOT: start-group
>>  // TEST1-NOT: "-lgcc"
>>  // TEST1-NOT: "-lc"
>> Index: clang/lib/Driver/ToolChains/Gnu.cpp
>> ===================================================================
>> --- clang/lib/Driver/ToolChains/Gnu.cpp
>> +++ clang/lib/Driver/ToolChains/Gnu.cpp
>> @@ -518,7 +518,8 @@
>>        if (Args.hasArg(options::OPT_fsplit_stack))
>>          CmdArgs.push_back("--wrap=pthread_create");
>>
>> -      CmdArgs.push_back("-lc");
>> +      if (!Args.hasArg(options::OPT_nolibc))
>> +        CmdArgs.push_back("-lc");
>>
>>        // Add IAMCU specific libs, if needed.
>>        if (IsIAMCU)
>>
>>
>>
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