Symbol table
From Wikipedia, the free encyclopedia
In computer science, a symbol table is a data structure used by a language translator such as a compiler or interpreter, where each identifier in a program's source code is associated with information such as its type, scope level and sometimes its location.
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[edit] Implementation
A hash table implementation of a symbol table is common and the table is usually maintained throughout all phases of translation. A compiler can use one large symbol table for all symbols or use separated, hierachical symbol tables for different scopes.
[edit] Uses
A symbol table is included as part of every object code file. During the linking of different object files, it is the linker's responsibility to handle any unresolved references.
A symbol table usually has a transient structure used only during a language translation process and then discarded, or sometimes it can be embedded in the output of that process for later exploitation, for example, during an interactive debugging session, or as a resource for formatting a diagnostic report during or after execution of a program.
[edit] Example
This is how a symbol table of a small program generated from the GNU binutils nm looks like, there is one data:holaamigosh ( assigned by D ), many functions ( self defined as well as from the standard library ). The first column is where the symbol is located in the memory, the second is "The symbol type" and the third is the name of the symbol. By passing suitable parameters, the symbol table was made to sort on basis of address.
00000020 a T_BIT
00000040 a F_BIT
00000080 a I_BIT
20000004 t irqvec
20000008 t fiqvec
2000000c t InitReset
20000018 T _main
20000024 t End
20000030 T AT91F_US3_CfgPIO_useB
2000005c t AT91F_PIO_CfgPeriph
200000b0 T main
20000120 T AT91F_DBGU_Printk
20000190 t AT91F_US_TxReady
200001c0 t AT91F_US_PutChar
200001f8 T AT91F_SpuriousHandler
20000214 T AT91F_DataAbort
20000230 T AT91F_FetchAbort
2000024c T AT91F_Undef
20000268 T AT91F_UndefHandler
20000284 T AT91F_LowLevelInit
200002e0 t AT91F_DBGU_CfgPIO
2000030c t AT91F_PIO_CfgPeriph
20000360 t AT91F_US_Configure
200003dc t AT91F_US_SetBaudrate
2000041c t AT91F_US_Baudrate
200004ec t AT91F_US_SetTimeguard
2000051c t AT91F_PDC_Open
2000059c t AT91F_PDC_DisableRx
200005c8 t AT91F_PDC_DisableTx
200005f4 t AT91F_PDC_SetNextTx
20000638 t AT91F_PDC_SetNextRx
2000067c t AT91F_PDC_SetTx
200006c0 t AT91F_PDC_SetRx
20000704 t AT91F_PDC_EnableRx
20000730 t AT91F_PDC_EnableTx
2000075c t AT91F_US_EnableTx
20000788 T __aeabi_uidiv
20000788 T __udivsi3
20000884 T __aeabi_uidivmod
2000089c T __aeabi_idiv0
2000089c T __aeabi_ldiv0
2000089c T __div0
200009a0 D _data
200009a0 A _etext
200009a0 D holaamigosh
200009a4 A __bss_end__
200009a4 A __bss_start
200009a4 A __bss_start__
200009a4 A _edata
200009a4 A _end
