Re: [RFC PATCH] semihosting/arm-compat: remove heuristic softmmu SYS_HEAPINFO

[Alex Bennée]

Peter Maydell <peter.maydell@linaro.org> writes:

> On Tue, 1 Jun 2021 at 10:12, Alex Bennée <alex.bennee@linaro.org> wrote:
>>
>> The previous numbers were a guess at best. While we could extract the
>> information from a loaded ELF file via -kernel we could still get
>> tripped up by self decompressing or relocating code. Besides sane
>> library code has access to the same symbols in run time to make a
>> determination of the location of the heap.
>>
>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>> Cc: Andrew <astrauss11@gmail.com>
>> ---
>>  semihosting/arm-compat-semi.c | 19 ++++++++++---------
>>  1 file changed, 10 insertions(+), 9 deletions(-)
>
> This seems like a pretty good candidate for breaking existing
> working binaries. How much testing against different varieties of
> guest-code-using-semihosting have you done ?

None, which is why it's an RFC - but at least one user reported newlib
attempts to use the numbers we gave it rather than falling back to
numbers it knew from the build and getting it wrong. I suspect any code
that doesn't have a fallback path is getting it right more by luck than
judgement though. I'd be curious to hear of code that relies on the
numbers it gets from QEMU.

>
> thanks
> -- PMM


-- 
Alex Bennée