Error out on unsupported relocation entries

This applies to both the PowerPC and RISC-V architectures, both of which have
tricky relocation types that `elf-edit` does not currently support. See #39 for
more information.

src/Data/ElfEdit/Relocations/PPC32.hs

@@ -191,7 +191,7 @@ ppc32Reloc tp nm c = (tp, (nm, c))
 -- These values are derived from Figure 4-1 (Relocation Fields) of
 -- http://refspecs.linux-foundation.org/elf/elfspec_ppc.pdf.
 --
--- Note that the treatment of `low24` and `low14` here is not correct. See
+-- Note that some of these values are not currently supported. See
 -- https://github.com/GaloisInc/elf-edit/issues/39 for more information.
 
 none :: Int
@@ -204,10 +204,10 @@ word30 :: Int
 word30 = 30
 
 low24 :: Int
-low24 = 24
+low24 = error "low24 relocation entries not currently supported"
 
 low14 :: Int
-low14 = 14
+low14 = error "low14 relocation entries not currently supported"
 
 half16 :: Int
 half16 = 16

src/Data/ElfEdit/Relocations/PPC64.hs

@@ -455,7 +455,7 @@ ppc64Reloc tp nm c = (tp, (nm, c))
 -- These values are derived from Section 4.5.1 (Relocation Types) of
 -- https://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi-1.9.pdf.
 --
--- Note that the treatment of `low24` and `low14` here is not correct. See
+-- Note that some of these values are not currently supported. See
 -- https://github.com/GaloisInc/elf-edit/issues/39 for more information.
 
 none :: Int
@@ -471,10 +471,10 @@ word30 :: Int
 word30 = 30
 
 low24 :: Int
-low24 = 24
+low24 = error "low24 relocation entries not currently supported"
 
 low14 :: Int
-low14 = 14
+low14 = error "low14 relocation entries not currently supported"
 
 half16 :: Int
 half16 = 16

src/Data/ElfEdit/Relocations/RISCV.hs

@@ -303,32 +303,32 @@ word64 = 64
 -- 16-bit RVC instruction formats) of
 -- https://riscv.org/wp-content/uploads/2017/05/riscv-spec-v2.2.pdf.
 --
--- Note that the treatment of these variables is not correct. See
+-- Note that these values are not currently supported. See
 -- https://github.com/GaloisInc/elf-edit/issues/39 for more information.
 
 bType :: Int
-bType = 32
+bType = error "B-Type fields not currently supported"
 
 cbType :: Int
-cbType = 16
+cbType = error "CB-Type fields not currently supported"
 
 cjType :: Int
-cjType = 16
+cjType = error "CJ-Type fields not currently supported"
 
 iType :: Int
-iType = 32
+iType = error "I-Type fields not currently supported"
 
 sType :: Int
-sType = 32
+sType = error "S-Type fields not currently supported"
 
 uType :: Int
-uType = 32
+uType = error "U-Type fields not currently supported"
 
 jType :: Int
-jType = 32
+jType = error "J-Type fields not currently supported"
 
 uiType :: Int
-uiType = 32
+uiType = error "U+I-Type fields not currently supported"
 
 -- This is a variable-length encoding, and it's unclear how to support this at
 -- the moment.