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TLDR: Apple messed up again and broke POSIX compliance

luite ran into problems when he installed the latest Xcode update because the derived platform constants were off.

He provided me the output of nm -P ./includes/dist-derivedconstants/header/tmp.o which turned out to have numbers which didn't make sense:

_derivedConstantAP_STACK_SPLIM C 1025 0
_derivedConstantBITMAP_BITS_SHIFT C 7 0
_derivedConstantBLOCKS_PER_MBLOCK C 253 0
_derivedConstantBLOCK_SIZE C 4097 0
_derivedConstantCINT_SIZE C 5 0
_derivedConstantCLONG_LONG_SIZE C 9 0
_derivedConstantCLONG_SIZE C 9 0
_derivedConstantDOUBLE_SIZE C 9 0
_derivedConstantDYNAMIC_BY_DEFAULT C 2 0
...

Which with an older Xcode version would have looked like

_derivedConstantAP_STACK_SPLIM C 401 0
_derivedConstantBITMAP_BITS_SHIFT C 7 0
_derivedConstantBLOCKS_PER_MBLOCK C fd 0
_derivedConstantBLOCK_SIZE C 1001 0
_derivedConstantCINT_SIZE C 5 0
_derivedConstantCLONG_LONG_SIZE C 9 0
_derivedConstantCLONG_SIZE C 9 0
_derivedConstantDOUBLE_SIZE C 9 0
_derivedConstantDYNAMIC_BY_DEFAULT C 2 0
...

So obviously nm -P's output changed from hexadecimal to (non-compliant) decimal formatting of numbers.

For reference, here's how POSIX specifies the semantics of nm:

http://pubs.opengroup.org/onlinepubs/9699919799/utilities/nm.html

---

-P Write information in a portable output format, as specified in the STDOUT section.

1. ..

If the -P option is specified, the previous information shall be displayed using the following portable format. The three versions differ depending on whether -t d, -t o, or -t x was specified, respectively:

"%s%s %s %d %d\n", <library/object name>, <name>, <type>, <value>, <size>

"%s%s %s %o %o\n", <library/object name>, <name>, <type>, <value>, <size>

"%s%s %s %x %x\n", <library/object name>, <name>, <type>, <value>, <size>

1. ..

If -P is specified, but -t is not, the format shall be as if -t x had been specified.

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In the event that Apple can't be bothered to fix this bug (I've had bad experience with Apple and standard-compliance in the past, hence my pessimism) we could try to workaround by using nm -P -t x when building on OSX...

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Alternative workaround (since it turns out that Apple's nm violates POSIX even more than assumed by not even supporting nm -P -t x):

Have deriveConstants derive a known value, e.g. the value 0x1234 via char derivedConstantCONTROL_GROUP[1+0x1234];, and if the value for CONTROL_GROUP comes back as 18016 we know that we need to fixup all decimal-wrongly-as-hex parsed integers, if it comes back as 4660 we parsed correctly; any different value is a non-recoverable error

This would also serve as a general integrity check for //all// platforms