Fix for issue 97. Aligns all var_args on the strongest alignment constraint #98
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…traints (long/pointer) so that var_args callers and callees use the same rules
Codecov Report
@@ Coverage Diff @@
## master #98 +/- ##
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Coverage 78.50% 78.51%
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Files 349 349
Lines 45526 45533 +7
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+ Hits 35741 35750 +9
+ Misses 9785 9783 -2
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This pull request does not cover another current problem: it is not possible to pass struct args to a varrarg function. It should be easy to fix: ths fix puts each argument in a slot and increments the pointer by the slot size. I propose that we fix the printf & co problem now (scanf & co are not a problem since they use only pointers) and deal with the minor restriction for struct later. |
…e to merge: select only objectfiles defining globally at least one yet unresolved symbol
… supported in initializer constants. Also extend the integer operations to enum types (which are integer types). Does not fix for & (address of)
| alignment = max(alignment, va_alignment) | ||
| # each argument is stored in a slot, aligned on the strongest alignment | ||
| size = self.va_alignment * len(var_args) | ||
| alignment = self.va_alignment |
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How about structs larger than the va_alignment size, is this allowed? Or can only basic types be passed via vararg way?
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There is no type restrictions in the C standard, although I have never seen composite types passed to vararg functions.
Struct/union are possible since they support argument-passing by value, and assignment.
In function calls; we can copy their value starting at one slot and occupying several slots. After the copy we realign the vararg pointer to the beginning of next slot.
In va_arg macro, we use assignment to get the value, we increment the vararg pointer by the type size + the required padding to realign the vararg pointer to the beginning of next slot.
| @@ -250,6 +255,11 @@ def has_symbol(self, name): | |||
| """ Check if this object file has a symbol with name 'name' """ | |||
| return name in self.symbol_map | |||
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| def is_defined_global(self, name): | |||
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I would rename this to defines_global
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Yes, that's more consistent.
The var_arg block is an array of slots, one for each argument.
The size of the slot is based on the strongest alignment between "long int" and pointers.
Each argument is stored at the address of its slot.
This way va_arg takes the expected value at the current var_arg pointer and increments it by the slot size.
On x86_64, the slot size is 8byte.
On i386, MIPS, m68k, the slot size is 4byte.