file-needed/recurive does not canonicalize paths

Hi,

(CC-ing Ludo, who wrote the code according to git logs)

during testing of wip-haskell I observed the make-dynamic-linker-cache

phase is taking alot of time (up to two minutes on a fast machine with

SSD). Looking at ghc-hindent for example [1]:

starting phase `make-dynamic-linker-cache'

created '/gnu/store/2nrzbaxmqs2rq9yv52bpyn2azb3qj6h1-ghc-hindent-5.3.4/etc/ld.so.cache' from 10085 library search path entries

phase `make-dynamic-linker-cache' succeeded after 119.5 seconds

And while Haskell packages link to a pretty large number of dynamic

libraries (116 in this case), 10000 search path entries seems wrong. Running just

(file-needed/recursive "/gnu/store/2nrzbaxmqs2rq9yv52bpyn2azb3qj6h1-ghc-hindent-5.3.4/bin/hindent")

takes a long time and reveals entries like

/gnu/store/1cyk8j2nd6r0cvm6kx1408kd763yf8h5-ghc-9.2.5/lib/ghc-9.2.5/Cabal-3.6.3.0/../directory-1.3.6.2/../unix-2.7.2.2/../bytestring-0.11.3.1/../template-haskell-2.18.0.0/../pretty-1.1.3.6/../array-0.5.4.0/../base-4.16.4.0/../ghc-bignum-1.2/../ghc-prim-0.8.0/libHSghc-prim-0.8.0-ghc9.2.5.so

so it looks like it deduplicates values, but does not canonicalize

paths. A relatively straight-forward fix could be the following change,

but I don’t know if that would cause any issues, since canonicalize-path

throws an exception if the resulting path does not exist. It’s also

a world rebuild since pretty much any package uses this phase (and the

reason and I cannot test it on a larger scale).

---snip---

Hi Lars,

Lars-Dominik Braun <lars@6xq.net> skribis:

Right. Other arguments against systematic canonicalization: (1)

‘canonicalize-path’ is costly, (2) developers and tools might choose to

write ‘x/y/../z’ for a good reason and changing that could break their

expectations.

Can you see how we end up with those entries? These at DT_NEEDED

entries, not DT_RUNPATH, right?

If so, that probably means that ghc at some points invokes the linker

along the lines of:

ld -o hindent ../foo/../bar/../baz/libbaz.so

Could you check in build logs exactly how that executable gets linked?

Is there a way we could canonicalize there, or, better, get the build

system to do something like:

ld -o hindent -L ../foo/../bar/../baz -lbaz

? That way DT_NEEDED would be just “libbaz.so” instead of the complete

file name. DT_RUNPATH would contain the weird file name, but that’s

probably okay.

HTH,

Ludo’.

Hi Ludo,

they definitely do not come from the hindent binary. `readelf -d` looks

like this

---snip---

0x0000000000000001 (NEEDED) Shared library: [libHSpath-io-1.7.0-Y7nuUr9RcCC0rgElOk2Zd-ghc9.2.5.so]

0x0000000000000001 (NEEDED) Shared library: [libHSunix-compat-0.5.4-2Fa5hW7FPv81iCQxP5gtt5-ghc9.2.5.so]

0x0000000000000001 (NEEDED) Shared library: [libHStemporary-1.3-K9lHfUrZ43CE7BhnE8cSVB-ghc9.2.5.so]

…

0x000000000000001d (RUNPATH) Library runpath: [/gnu/store/2nrzbaxmqs2rq9yv52bpyn2azb3qj6h1-ghc-hindent-5.3.4/lib/x86_64-linux-ghc-9.2.5:/gnu/store/1cyk8j2nd6r0cvm6kx1408kd763yf8h5-ghc-9.2.5/lib/ghc-9.2.5/Cabal-3.6.3.0:/gnu/store/lk1mgbds7rf9ilv425msz840ky8cfn79-ghc-diff-0.4.1/lib/x86_64-linux-ghc-9.2.5:/gnu/store/866s8qcghallds7azzcx075a06mr64h4-ghc-hunit-1.6.2.0/lib/x86_64-linux-ghc-9.2.5:/gnu/store/rgm9h2a4v1zgwm1mbfb36ycjbkywlxj6-ghc-onetuple-0.3.1/lib/x86_64-linux-ghc-9.2.5:…

---snap---

and I believe GHC adds `-L/gnu/store/…` and `-lHSXXX` to the linker

invokation only, which should be correct. However GHC’s

bundled libraries are linked differently and result in a `readelf -d

/gnu/store/1cyk8j2nd6r0cvm6kx1408kd763yf8h5-ghc-9.2.5/lib/ghc-9.2.5/Cabal-3.6.3.0/libHSCabal-3.6.3.0-ghc9.2.5.so`

like this:

---snip---

0x0000000000000001 (NEEDED) Shared library: [libHSprocess-1.6.16.0-ghc9.2.5.so]

0x0000000000000001 (NEEDED) Shared library: [libHSparsec-3.1.15.0-ghc9.2.5.so]

0x0000000000000001 (NEEDED) Shared library: [libHStext-1.2.5.0-ghc9.2.5.so]

…

0x000000000000001d (RUNPATH) Library runpath: [$ORIGIN/../process-1.6.16.0:$ORIGIN/../parsec-3.1.15.0:$ORIGIN/../text-1.2.5.0:$ORIGIN/../mtl-2.2.2:$ORIGIN/../transformers-0.5.6.2:$ORIGIN/../directory-1.3.6.2:$ORIGIN/../unix-2.7.2.2:$ORIGIN/../time-1.11.1.1:$ORIGIN/../filepath-1.4.2.2:$ORIGIN/../binary-0.8.9.0:$ORIGIN/../containers-0.6.5.1:$ORIGIN/../bytestring-0.11.3.1:$ORIGIN/../template-haskell-2.18.0.0:$ORIGIN/../pretty-1.1.3.6:$ORIGIN/../ghc-boot-th-9.2.5:$ORIGIN/../deepseq-1.4.6.1:$ORIGIN/../array-0.5.4.0:$ORIGIN/../base-4.16.4.0:$ORIGIN/../ghc-bignum-1.2:$ORIGIN/../ghc-prim-0.8.0:$ORIGIN/../rts:/gnu/store/5h2w4qi9hk1qzzgi1w83220ydslinr4s-glibc-2.33/lib:/gnu/store/094bbaq6glba86h1d4cj16xhdi6fk2jl-gcc-10.3.0-lib/lib:/gnu/store/fwbiihd2sbhai63y1pvvdh0f2bakfzrf-gmp-6.2.1/lib:/gnu/store/094bbaq6glba86h1d4cj16xhdi6fk2jl-gcc-10.3.0-lib/lib/gcc/x86_64-unknown-linux-gnu/10.3.0/../../..]

---snap---

These obviously will get expanded to

/gnu/store/1cyk8j2nd6r0cvm6kx1408kd763yf8h5-ghc-9.2.5/lib/ghc-9.2.5/Cabal-3.6.3.0/../process-1.6.16.0

And there’s about 40 of these bundled libraries referencing each other,

which is why the problem is amplified.

I still believe this is a bug in file-needed/recursive, because it

recurses, but does not correctly keep track of “visited” shared

libraries (by not canonicalizing paths). Its documentation also says

that it returns a “list of absolute .so file names” – which I

would expect not to have relative path elements in. The output of `ldd`

does so too. So yes, canonicalize-path may be expensive, but evaluating

10000 shared libraries is too.

Cheers,

Lars

PS: This is not a problem for wip-haskell any more, since I switched to

static linking, but it’s going to bite someone else.