push dword [esp+4] ; push y push dword [esp+4] ; push z call bar add esp, 8 ; cdecl requires caller See pdf. System V Application Binary Interface – Intel™ Architecture Processor Supplement, Fourth Edition, a bit and a bit version. The bit version of standard can be found at and the 64bit version.
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Index of /pub/linux/mips/doc/ABI
Comment 5 Alexandre Pereira Nunes Bug Watch Updater bug-watch-updater on Gcc defaults to bit alignment for stack Date: I am talking about the actual, runtime stack parameters abi86 the machine level and whether or not those stack locations can be modified be the callee.
How C code behaves and how the calling conventions work can be quite different. Post as a guest Name. Yes, the callee can modify the arguments on the stack.
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I understand perfectly that using structures like that is meant to be non-portable, but it’s quite handy to have something like that without too much worry about platforms, since altough I develop for several arches, almost all of them today have a gcc port, and I know there are others with similar issues. Uninterrupted Lectures and Labs until Thanksgiving!
I didn’t expect the type change ab386 force an alignment. The caller does clean them up but ignores the value. Inside the function, you decide that for clarity, you will create another structure and set it “equal” to the first one, and only operate on the new one from now on.
linux – C calling conventions and passed arguments – Stack Overflow
When a bit-field is inserted into a packed record, the whole size of the underlying type is used by one or more same-size adjacent bit-fields that is, if its long: Comment 9 Richard Biener Although the caller in some calling conventions is the one that cleans up the arguments, all it’s really doing is deallocating the space previously allocated on the stack to hold the argument values.
Berry 1, 1 8 Yes in practice an arguments might never actually be in any kind of stack, it would be in a named register this is especially true in platforms with a lot of registers – like MIPS.
He’s helping author a new ABI supplement for ‘x32’, a 32 bit x abi; see https: M and T No Classes. Calendar This week M-F Sept Lara Dougan 3 As far as the callee is concerned, they are the same as local variables. Email me about changes to this bug report. Email Required, but never shown.
Since it is very unlikely for gcc to default to 32bit stack alignment, it is highly recommended that functions should have stack aligned at bit before calling functions generated by gcc.
Comment 2 Richard Biener Then the address of the variable is passed. More serious penalties for repeated cases: Please fix this in LSB 4. Is it a default on gcc whenever the target has no particular semantics as arm-elf, which I suppose does not derive from the ARM published ABIs at all? Top of the stack is located easily. If you pass by value: Launchpad couldn’t connect to lsbbugs. I was under the assumption that since the caller is the one that cleans them up, that they should contain the same values after the function call.
I have also looked for documentation including the System V i calling conventions, but was unable to find a definitive answer to this. Even TAs and profs can find them! Jeff Johnson n3npq on The argument is copied probably to the begining of the stack but maybe not depending on your compiler the celled program can mess with this copy as much as it wants but the variable in the clling program will not be changed. Even from the author!
It’s stated somewhere in gcc docs that gcc tries to do things uniformly, only diverging between targets where there’s a compelling reason to do so. Better documentation is certainly appreciated, but – what is the bug here? Comment 10 Alexandre Pereira Nunes If this revert to be a non-bug and I can still hold a feature request on it, I would be satisfied.
I do believe that ABI-conformant structures are always padded alignedand the packed structures are outside of the ABI scope This change means that functions in object files generated by gcc may not work correctly when called from object files which only guarantee 32bit stack alignment.
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C calling conventions and passed arguments Ask Question. I’ll create some additional creative questions. When making a function call in Linux or OS X for that mattercan the callee abi36 the values of the arguments on the stack? None, the status of the bug is updated manually. Called function needs to “know” how many parameters to use.
Greg Hewgill k The callee is free to modify the values during execution of the function, because the caller isn’t going to look at their values later. Course grade downgrade, failure, report to graduate dean or undergrad. Although the agi386 does not require any alignment of the stack, software convention and the operating system requires that the stack be aligned on a word boundary.
Comment 7 Richard Biener