[cfe-dev] Clang tooling and cross compiled code bases

[Manuel Klimek]

On Mon, Sep 10, 2012 at 6:15 AM, Andrew McGregor <andrewmcgr at gmail.com> wrote:
>
> On 10/09/2012, at 12:43 PM, Andrew McGregor <andrewmcgr at gmail.com> wrote:
>
>>
>> On 7/09/2012, at 8:57 PM, Manuel Klimek <klimek at google.com> wrote:
>>
>>> On Fri, Sep 7, 2012 at 3:36 AM, Andrew McGregor <andrewmcgr at gmail.com> wrote:
>>>> I have an issue where I'm trying to use a libTooling based refactoring tool on a codebase that is intended for cross-compilation.  I have hacked together means to create a compile_commands.json, but the tool is ignoring -triple and -internal-isystem and therefore getting the sizes of many basic types wrong since my compile host is 64 bit and the target isn't.
>>>>
>>>> Is there a straightforward way of resolving this?
>>>
>>> I'd say: it's a bug :) Is there an easy way to reproduce this in a
>>> small example?
>>
>> I'll try to construct one.  Don't hold your breath, this is a background job.
>>
>> Andrew
>
> Ok, I did get time, so here we go.  Given compile_commands.json containing (obviously, change paths as appropriate):
>
> [
>     {
>         "command": "clang -fno-signed-char -c -o foo.o foo.c",
>         "directory": "/home/andrewm/source/hack/minimal-clang-cc-problem",
>         "file": "/home/andrewm/source/hack/minimal-clang-cc-problem/foo.c",
>     },
> ]
>
> and foo.c in the appropriate place containing:
>
> #include <stdio.h>
> #include <stdint.h>
>
> void oinker(char *it) {
>   printf("%s\n", it);
> }
>
> int main(int argc, char **argv) {
>   uint64_t foo;
>   uint8_t oink[] = "oink";
>
>   oinker(oink);
>   return 0;
> }
>
> $ clang-check -p=/home/andrewm/source/hack/minimal-clang-cc-problem/ /home/andrewm/source/hack/minimal-clang-cc-problem/foo.c
> Processing: /home/andrewm/source/hack/minimal-clang-cc-problem/foo.c.
> warning: argument unused during compilation: '-fno-signed-char'
> foo.c:12:10: warning: passing 'uint8_t [5]' to parameter of type 'char *' converts between pointers to integer types with different sign [-Wpointer-sign]
>   oinker(oink);
>          ^~~~
> foo.c:4:19: note: passing argument to parameter 'it' here
> void oinker(char *it) {
>                   ^
> 1 warning generated.
>
> I would argue that -fno-signed-char should be respected in this situation.
>
> The same sort of thing applies to many arguments, including -triple (but not -target) and -isystem-internal.

When I try to compile this (no tooling involved, just plain clang):
$ ~/build/llvm/bin/clang -c t2.c -fno-signed-char
clang-3: warning: argument unused during compilation: '-fno-signed-char'
<...>

According to chandlerc the right way to pass this to clang is to use
-funsigned-char. Unfortunately that doesn't make the code snippet
compile either:
$ ~/build/llvm/bin/clang -c t2.c -funsigned-char
t2.c:12:10: warning: passing 'uint8_t [5]' to parameter of type 'char
*' converts between pointers to integer types with different sign
[-Wpointer-sign]
<...>

So, that doesn't really seem to be a reduction of the problem you're seeing.

-internal-isystem (I assume you meant that instead of
"-isystem-internal") is a red herring, too - it shouldn't be in a
compilation database, it's an internal flag.

Cheers,
/Manuel