Geert Uytterhoeven dixit: >Should these be truncated to 32-bit explicitly, or is this a bug in mksh? mksh in “mksh mode” operates specifically on 32-bit integer data types with defined wraparound and other guarantees beyond what POSIX does. There is an “lksh” binary in the mksh binary package in Debian and derivates now, which is the “legacy mode” that uses the host system’s “long” data type, as POSIX demands, and is now (mksh_46-2) used for /bin/sh. However, on mixed 32/64-bit systems, /bin/sh can have either bit size. Additionally, it is not possible, in POSIX, without invoking ISO C “Undefined Behaviour”, to find out the bitsize of the shell arithmetics. Furthermore, Linux can be cross-compiled, so when building kernels for 64-bit platforms on 32-bit systems, the arithmetics used MUST NOT overflow beyond a signed 32-bit “long”. > [1/3] h8300/boot: Use POSIX "$((..))" instead of bashism "$[...]" > [2/3] ARM: shmobile: Use POSIX "$((..))" instead of bashism "$[...]" > [3/3] sh/boot: Use POSIX "$((..))" instead of bashism "$[...]" Independent of the above, I’ve verified all three and can state that they ⓐ are no regression relative to existing behaviour ⓑ do not invoke any features not in POSIX $((…)) arithmetics ⓒ do not invoke any features not in mksh $((…)) arithmetics This means you can add my Signed-off: Thorsten Glaser <tg@xxxxxxxxxx> However, I urge you to check whether any of these arithmetics can go beyond 32 bit. If they have even the slightest chance to do that, you MUST replace them by something different. One method could be to use bc(1): $(shell printf 'obase=16\nibase=16\n%s+%s\n' $(FOO) $(BAR) | bc) Another method could be to operate on the upper half and the lower half of the 64-bit quantities separately, assuming that calculations do not overflow (in POSIX sh, overflow is, like in ISO C, Undefined Behaviour; a C compiler is permitted to compile the source code in the shell that invokes it to run “rm -rf ~ /” instead) or carry over (e.g. if it’s known that the first half is always 0x7FFFFFFF or the last half always 00000000 you can just add that as “string”). bye, //mirabilos -- FWIW, I'm quite impressed with mksh interactively. I thought it was much *much* more bare bones. But it turns out it beats the living hell out of ksh93 in that respect. I'd even consider it for my daily use if I hadn't wasted half my life on my zsh setup. :-) -- Frank Terbeck in #!/bin/mksh -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
