[Haskell-cafe] possible bug in latest hackage Elf (Elf-0.27)

[Baojun Wang]

re-format patch:

--
--- a/Elf.hs    2012-12-04 19:27:51.000000000 -0800
+++ b/Elf.hs    2014-05-14 23:47:08.565983310 -0700
@@ -666,12 +666,12 @@ getSymbolTableEntries e s =
 -- If the size is zero, or the offset larger than the 'elfSectionData',
 -- then 'Nothing' is returned.
 findSymbolDefinition :: ElfSymbolTableEntry -> Maybe B.ByteString
-findSymbolDefinition e =
-    let enclosingData = fmap elfSectionData (steEnclosingSection e)
-        start = fromIntegral (steValue e)
+findSymbolDefinition e = steEnclosingSection e >>= \enclosingSection ->
+    let enclosingData = elfSectionData enclosingSection
+        start = ( (fromIntegral (steValue e)) - (fromIntegral
(elfSectionAddr enclosingSection) ) )
         len = fromIntegral (steSize e)
-        def = fmap (B.take len . B.drop start) enclosingData
-    in if def == Just B.empty then Nothing else def
+        def = (B.take len . B.drop start) enclosingData
+    in if def == B.empty then Nothing else Just def

 runGetMany :: Get a -> L.ByteString -> [a]
 runGetMany g bs
@@ -712,7 +712,7 @@ getSymbolTableEntry e strtlb =
     return $ EST (nameIdx,name) sec typ bind other sTlbIdx symVal size

 sectionByIndex :: Elf -> ElfSectionIndex -> Maybe ElfSection
-sectionByIndex e (SHNIndex i) = lookup i . zip [1..] $ (elfSections e)
+sectionByIndex e (SHNIndex i) = lookup i . zip [0..] $ (elfSections e)
 sectionByIndex _ _ = Nothing

 infoToTypeAndBind :: Word8 -> (ElfSymbolType,ElfSymbolBinding)

--

http://github.com/erikcharlebois/elf gives 404.

Thanks
Baojun


On Wed, May 14, 2014 at 11:18 PM, Baojun Wang <wangbj at gmail.com> wrote:

> Hi list,
>
> with below test program:
>
> --
> ​/* test1.c: build with -g -O0 */
> include <stdio.h>
>
> static const char appmsg[] = "hello, world";
>
> int main(int argc, char* argv[])
> {
>         fputs(appmsg, stdout);
>
>         return 0;
> }
>
>
> --- elf-test1.hs
> module Main where
>
> import qualified Data.ByteString as B
> import qualified Data.ByteString.Char8 as C
>
> import Control.Monad
>
> import Data.Elf
>
> testelf = "/tmp/test1"
> testelfsym = C.pack "appmsg"
>
> lookupSymbol1 _ [] = Nothing
> lookupSymbol1 sym (t:ts) =
>    case (snd (steName t)) of
>      Nothing -> lookupSymbol1 sym ts
>      Just sname -> if sname == sym then Just t
>                    else lookupSymbol1 sym ts
>
> lookupSymbol _ [] = Nothing
> lookupSymbol sym (t:ts) =
>   case (lookupSymbol1 sym t) of
>     Nothing -> lookupSymbol sym ts
>     t1 -> t1
>
> test1 elf symtab symbol = mapM_ (print) (elfSections elf)
>
> test2 elf symtab symbol =
>   lookupSymbol symbol symtab
>
> test3 elf symtab symbol =
>   lookupSymbol symbol symtab >>= \et ->
>   findSymbolDefinition et
>
> mainloop elf symtab symbol =
> --  (test1 elf symtab symbol) >>
>   print (test2 elf symtab symbol) >>
>   print (test3 elf symtab symbol) >>
>   return ()
>
> main = do
>   contents <- B.readFile testelf
>   let elf = parseElf contents
>       symtab = parseSymbolTables elf
>   mainloop elf symtab testelfsym
> ---
>
> the latest Data.Elf doesn't geive correct output as expected:
>
> output will be:
>
> Just (EST {steName = (9,Just "appmsg"), steEnclosingSection = Just
> (ElfSection {elfSectionName = ".fini", elfSectionType = SHT_PROGBITS,
> elfSectionFlags = [SHF_EXECINSTR,SHF_ALLOC], elfSectionAddr = 4195908,
> elfSectionSize = 9, elfSectionLink = 0, elfSectionInfo = 0,
> elfSectionAddrAlign = 4, elfSectionEntSize = 0, elfSectionData =
> "H\131\236\bH\131\196\b\195"}), steType = STTObject, steBind = STBLocal,
> steOther = 0, steIndex = SHNIndex 14, steValue = 4195924, steSize = 13})
>
> From above, you can see the steEnclosingSection is wrong and offset by 1.
>
> The *correct* output should be:
> Just (EST {steName = (9,Just "appmsg"), steEnclosingSection = Just
> (ElfSection {elfSectionName = ".rodata", elfSectionType = SHT_PROGBITS,
> elfSectionFlags = [SHF_ALLOC], elfSectionAddr = 4195920, elfSectionSize =
> 17, elfSectionLink = 0, elfSectionInfo = 0, elfSectionAddrAlign = 4,
> elfSectionEntSize = 0, elfSectionData = "\SOH\NUL\STX\NULhello,
> world\NUL"}), steType = STTObject, steBind = STBLocal, steOther = 0,
> steIndex = SHNIndex 14, steValue = 4195924, steSize = 13})
> Just "hello, world\NUL"
>
> After check Elf.hs, I found there could be two issues:
> 1) in sectionByIndex, (SHNIndex) should start from 0, not 1; this cause
> the steEnclosingSection from my exmaple offset by 1;
> 2) in findSymbolDefinition, start should substract the sectionAddr (base
> address).
>
> please see below diff for details:
>
> --
>
> --- a/Elf.hs   2012-12-04 19:27:51.000000000 -0800
> +++ b/Elf.hs      2014-05-14 22:57:01.014498515 -0700
> @@ -1,5 +1,5 @@
>  -- | Data.Elf  is a module for parsing a ByteString of an ELF file into
> an Elf record.
> -module Data.Elf ( parseElf
> +module Elf ( parseElf
>                  , parseSymbolTables
>                  , findSymbolDefinition
>                  , Elf(..)
> @@ -666,12 +666,12 @@ getSymbolTableEntries e s =
>  -- If the size is zero, or the offset larger than the 'elfSectionData',
>  -- then 'Nothing' is returned.
>  findSymbolDefinition :: ElfSymbolTableEntry -> Maybe B.ByteString
> -findSymbolDefinition e =
> -    let enclosingData = fmap elfSectionData (steEnclosingSection e)
> -        start = fromIntegral (steValue e)
> +findSymbolDefinition e = steEnclosingSection e >>= \enclosingSection ->
> +    let enclosingData = elfSectionData enclosingSection
> +        start = ( (fromIntegral (steValue e)) - (fromIntegral
> (elfSectionAddr enclosingSection) ) )
>          len = fromIntegral (steSize e)
> -        def = fmap (B.take len . B.drop start) enclosingData
> -    in if def == Just B.empty then Nothing else def
> +        def = (B.take len . B.drop start) enclosingData
> +    in if def == B.empty then Nothing else Just def
>
>  runGetMany :: Get a -> L.ByteString -> [a]
>  runGetMany g bs
> @@ -712,7 +712,7 @@ getSymbolTableEntry e strtlb =
>      return $ EST (nameIdx,name) sec typ bind other sTlbIdx symVal size
>
>  sectionByIndex :: Elf -> ElfSectionIndex -> Maybe ElfSection
> -sectionByIndex e (SHNIndex i) = lookup i . zip [1..] $ (elfSections e)
> +sectionByIndex e (SHNIndex i) = lookup i . zip [0..] $ (elfSections e)
>  sectionByIndex _ _ = Nothing
>
>  infoToTypeAndBind :: Word8 -> (ElfSymbolType,ElfSymbolBinding)
>
> --
>
> Would you please check above change and update Data.Elf hackage? I cannot
> find the author from http://hackage.haskell.org/package/elf-0.27
>
> Thanks
> baojun
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20140515/9b8c37a4/attachment.html>