better file/line info for format string errors in trace events

better file/line info for format string errors in trace events

[Peter Maydell]

If you have a format string error in a trace event it fails
like this:

In file included from ../../hw/block/trace.h:1:0,
                 from ../../hw/block/fdc.c:48:
./trace/trace-hw_block.h: In function '_nocheck__trace_pci_nvme_err_mdts':
./trace/trace-hw_block.h:2162:18: error: format '%llu' expects
argument of type 'long long unsigned int', but argument 6 has type
'size_t {aka unsigned int}' [-Werror=format=]
         qemu_log("%d@%zu.%06zu:pci_nvme_err_mdts " "cid %"PRIu16" len
%"PRIu64"" "\n",
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/peter.maydell/qemu/include/qemu/osdep.h:89:0,
                 from ../../hw/block/fdc.c:30:
/usr/include/inttypes.h:105:34: note: format string is defined here
 # define PRIu64  __PRI64_PREFIX "u"


which doesn't anywhere give the filename where the format
string is actually defined (hw/block/trace-events in this case),
let alone the line number in that file of the trace event.

Bit of a long shot, but I don't suppose it's possible for the
tracing subsystem to give more targeted error messages in this
situation ?

thanks
-- PMM

Re: better file/line info for format string errors in trace events

[Stefan Hajnoczi]

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On Tue, Aug 25, 2020 at 10:49:08PM +0100, Peter Maydell wrote:
> If you have a format string error in a trace event it fails
> like this:
> 
> In file included from ../../hw/block/trace.h:1:0,
>                  from ../../hw/block/fdc.c:48:
> ./trace/trace-hw_block.h: In function '_nocheck__trace_pci_nvme_err_mdts':
> ./trace/trace-hw_block.h:2162:18: error: format '%llu' expects
> argument of type 'long long unsigned int', but argument 6 has type
> 'size_t {aka unsigned int}' [-Werror=format=]
>          qemu_log("%d@%zu.%06zu:pci_nvme_err_mdts " "cid %"PRIu16" len
> %"PRIu64"" "\n",
>                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> In file included from /home/peter.maydell/qemu/include/qemu/osdep.h:89:0,
>                  from ../../hw/block/fdc.c:30:
> /usr/include/inttypes.h:105:34: note: format string is defined here
>  # define PRIu64  __PRI64_PREFIX "u"
> 
> 
> which doesn't anywhere give the filename where the format
> string is actually defined (hw/block/trace-events in this case),
> let alone the line number in that file of the trace event.
> 
> Bit of a long shot, but I don't suppose it's possible for the
> tracing subsystem to give more targeted error messages in this
> situation ?

I will send a patch to make tracetool emit #line directives:
https://gcc.gnu.org/onlinedocs/gcc-10.2.0/cpp/Line-Control.html

Stefan

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