Re: [Xen-devel] staging GCC 8.1.0 build warnings

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, May 10, 2018 at 09:38:26AM +1000, John Thomson wrote:
> Hi,
> Trying to build Xen staging with GCC 8.1.0 and facing some of the new 
> warnings:
> 
> For OVMF, I used these three commits:
> https://github.com/tianocore/edk2/compare/1d212a83df0eaf32a6f5d4159beb2d77832e0231^...9de306701312f986c9638cb819d3f1f848d55cab.patch
> 1d212a83df0eaf32a6f5d4159beb2d77832e0231
> 9222154ae7b3eef75ae88cdb56158256227cb929
> 9de306701312f986c9638cb819d3f1f848d55cab
> 
> 
> For IPXE, one of these patches:
> http://lists.ipxe.org/pipermail/ipxe-devel/2018-April/006146.html
> https://build.opensuse.org/package/view_file/openSUSE:Factory/qemu/ipxe-efi-guard-strncpy-with-gcc-warning-ignore-pragma.patch?expand=1
> 
> I was still unable to build IPXE at the Xen selected commit in 
> tools/firmware/etherboot/Makefile:IPXE_GIT_TAG, with Errors:
> [BUILD] bin/netdevice.o
> Assembler messages
> junk at end of line, first unrecognized character is `@'
> can't resolve `__table_entries.2720' {.tbl.net_device_configurators.99 
> section} - `__table_entries.2722' {.tbl.net_device_configurators.00 section}
> can't resolve `__table_entries.2796' {.tbl.net_device_configurators.99 
> section} - `__table_entries.2798' {.tbl.net_device_configurators.00 section}
> 
> I ended up using IPXE master and the OpenSUSE 
> ipxe-efi-guard-strncpy-with-gcc-warning-ignore-pragma.patch
> I have not followed this up to find which commit fixes my build yet.
> 
> How close to ready are the standalone IPXE patches?

It has gathered some comments. v2 is not yet posted. At this point it is
definitely N+1 material.

I don't think having it merged in N+1 will be a big problem though,
provided we find enough bandwidth to work on it.

> 
> For QEMU, this commit:
> https://github.com/qemu/qemu/commit/84c868f6b8f8c1be9d3d65df93cf00b30821401c.patch
> 84c868f6b8f8c1be9d3d65df93cf00b30821401c
> 
> 
> In tools/ocaml/libs/xc/xenctrl_stubs.c
> char error_str[1028];
> 
>  CC       xenctrl_stubs.o
> xenctrl_stubs.c: In function 'failwith_xc':
> xenctrl_stubs.c:65:17: error: 'snprintf' output may be truncated before the 
> last format character [-Werror=format-truncation=]
>       "%d: %s: %s", error->code,
>                  ^
> xenctrl_stubs.c:64:4: note: 'snprintf' output 6 or more bytes (assuming 1029) 
> into a destination of size 1028
>     snprintf(error_str, sizeof(error_str),
>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>       "%d: %s: %s", error->code,
>       ~~~~~~~~~~~~~~~~~~~~~~~~~~
>       xc_error_code_to_desc(error->code),
>       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>       error->message);
>       ~~~~~~~~~~~~~~~
> cc1: all warnings being treated as errors
> 
> I changed these, but am not sure if this is correct?
> char error_str[XC_MAX_ERROR_MSG_LEN + 6]
> sizeof(error_str) - 1 in the three snprintf

Bumping the size should be fine.

> 
> 
> /build/xen-git/src/xen/stubdom/tpm_emulator-x86_64/tpm/tpm_deprecated.c:437:7:
>  error: 'memcmp' reading 20 bytes from a region of size 8 
> [-Werror=stringop-overflow=]
>    if (memcmp(&b1, &newAuthLink, sizeof(TPM_HMAC))) {
>        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Not sure how to approach this, I disabled the vtpm stubdoms in my builds for 
> now.
> 

If you don't use it, disabling it is the best option.

Wei.

> 
> 
> Cheers,
> -- 
>   John Thomson
> 
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