Re: Any known way to build devel/llvm* ( such as devel/llvm19 ) with --threads=1 for its linker activity during the build?

On Aug 4, 2024, at 14:31, Mark Millard <[email protected]> wrote:

> On Aug 3, 2024, at 23:07, Mark Millard <[email protected]> wrote:
> 
>> My recent attempts to build devel/llvm18 and devel/llvm19 in an armv7 context (native or aarch64-as-armv7) have had /usr/bin/ld failures that stop the build and report as:
>> 
>> LLVM ERROR: out of memory
>> Allocation failed
>> 
>> (no system OOM activity or notices, so just a process size/fragmentation issue, or so I would expect).
>> 
>> On native armv7 I also had rust 1.79.0 fail that way so --but aarch64-as-armv7 built it okay.
>> 
>> I'm curious if --threads=1 use for the linker might allow the devel/llvm* builds to complete at this point. Similarly for rust. (top showed that the ld activity was multi-threaded.)
>> 
>> Note: The structure of the poudriere-devel based native build attempts is historical and it used to work. Similarly for the aarch64-as-armv7 based build attempts. For now I'd just be exploring changes that might allow much of my historical overall structure to still work. But I expect that things are just growing to the point building is starting to be problematical with process address spaces that are bounded by a limit somewhat under 4 GiBytes.
>> 
>> 
>> Native armv7 was a 2 GiByte OrangePi+ 2ed (4 cores) that had
>> at boot time:
>> 
>> AVAIL_RAM+SWAP == 1958Mi+3685Mi == 5643Mi
>> 
>> and later had "Max(imum)Obs(erved)" figures:
>> 
>> Mem: . . .,
>> 1728Mi MaxObsActive, 275192Ki MaxObsWired, 1952Mi MaxObs(Act+Wir+Lndry)
>> 
>> Swap: 3685Mi Total, . . .,
>> 1535Mi MaxObsUsed, 3177Mi MaxObs(Act+Lndry+SwapUsed),
>> 3398Mi MaxObs(A+Wir+L+SU), 3449Mi (A+W+L+SU+InAct)
>> 
>> 
>> The aarch64-as-armv7 was a Win DevKit 2023 that has 8 cores and:
>> 
>> AVAIL_RAM+SWAP == 31311Mi+120831Mi == 152142Mi
>> 
>> So lots of 4 GiByte or smaller processes would fit.
>> 
> 
> Absent finding a way to get --threads=1 to be what is used, I
> made the following crude way to test, built it, installed it
> in the armv7 directory tree used for aarch64-as-armv7, and
> then started an aarch64-as-armv7 test of building devel/llvm19
> to see what the consequences are (leading whitespace details
> might not be preserved):
> 
> # git -C /usr/main-src/ diff contrib/llvm-project/
> diff --git a/contrib/llvm-project/lld/ELF/Driver.cpp b/contrib/llvm-project/lld/ELF/Driver.cpp
> index 8b2c32b15348..299daf7dd6fa 100644
> --- a/contrib/llvm-project/lld/ELF/Driver.cpp
> +++ b/contrib/llvm-project/lld/ELF/Driver.cpp
> @@ -1587,6 +1587,9 @@ static void readConfigs(opt::InputArgList &args) {
>             arg->getValue() + "'");
>     parallel::strategy = hardware_concurrency(threads);
>     config->thinLTOJobs = v;
> +  } else if (sizeof(void*) <= 4) {
> +    log("set maximum concurrency to 1, specify --threads= to change");
> +    parallel::strategy = hardware_concurrency(1);
>   } else if (parallel::strategy.compute_thread_count() > 16) {
>     log("set maximum concurrency to 16, specify --threads= to change");
>     parallel::strategy = hardware_concurrency(16);
> 
> Basically, if the process address space has to be "small", avoid
> any default memory use tradeoffs that multi-threading the linker
> might involve --even if that means taking more time.
> 
> We will see if:
> 
> [00:00:33] [07] [00:00:00] Building   devel/llvm19@default | llvm19-19.1.0.r1
> 
> still fails to build as armv7 vs. if the change leads it to
> manage to build as armv7.

The link attempt for "-o bin/llvm-exegesis" still failed:

LLVM ERROR: out of memory
Allocation failed


A potentially interesting note is that:

https://llvm.org/docs/CommandGuide/llvm-exegesis.html

reports:

QUOTE
llvm-exegesis currently only supports X86 (64-bit only), ARM (AArch64 only), MIPS, and PowerPC (PowerPC64LE only) on Linux for benchmarking. Not all benchmarking functionality is guaranteed to work on every platform. llvm-exegesis also has a separate analysis mode that is supported on every platform that LLVM is.
END QUOTE


===
Mark Millard
marklmi at yahoo.com