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vvuk
Joined: 25 Apr 2005
Posts: 13
Location: Foster City, CA
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 Posted: Fri May 06, 2005 7:50 pm Post subject: ELF structures/sections |
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On loading an ELF or PRX, the PSP's loader has the ability to dynamically link in other prx modules. There's a couple of structures that are relevant to this; this is what i've deduced so far. nem has much of this in the startup.s in the HelloPSP source zip.
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typedef struct {
// 0, 0, 1, 1 ?
unsigned char c1, c2, c3, c4;
// 28 bytes of module name, packed with 0's.
char name[28];
unsigned long gp; /* ptr to MIPS GOT data */
unsigned long libent; /* ptr to .lib.ent section */
unsigned long libentend; /* ptr to end of .lib.ent section */
unsigned long libstub; /* ptr to .lib.stub section */
unsigned long libstubend; /* ptr to end of .lib.stub section */
} __attribute__((packed)) PspModuleInfo;
// this struct seems to appear as the data in
// the .lib.ent section, and is referenced by
// the module info
typedef struct {
unsigned long l1; // 0x00000000 ?
unsigned long l2; // 0x80000000, most likely flags ?
unsigned long l3; // 0x00010104, maybe 2 shorts? one is a version?
// addr of start of .rodata.sceResident, which has 4
// longs (and one 0 long) before module name strings start,
// which includes things like a ptr to _start (see PspResidentData struct)
unsigned long sceResidentAddr;
} PspLibEntData;
// this struct is pointed to by PspLibEntData, and appears at the
// start of .rodata.sceResident. Each entry in .rodata.sceResident
// has a null long in between it, with the module strings (used in
// LibStubEntry) being padded to 4-byte alignment, and always
// including a terminating 0.
typedef struct {
unsigned long l1; // unknown 0xd632acdb
unsigned long l2; // unknown 0xf01d73a7
unsigned long startAddress; // address of _start
unsigned long moduleInfoAddr; // address of sceModuleInfo struct
} PspResidentData;
typedef struct {
// pointer to module name (will be in .rodata.sceResident section)
unsigned long moduleNameSymbol;
// mod version??
unsigned short version;
unsigned short val1;
unsigned char val2; // 0x5
unsigned char val3;
// number of function symbols
unsigned short numFuncs;
// each symbol has an associated nid; nidData is a pointer
// (in .rodata.sceNid section) to an array of longs, one
// for each function, which identifies the function whose
// address is to be inserted.
//
// The hash is the first 4 bytes of a SHA-1 hash of the function
// name. (Represented as a little-endian long, so the order
// of the bytes is reversed.)
unsigned long nidData;
// the address of the function stubs where the function address jumps
// should be filled in
unsigned long firstSymAddr;
} __attribute__((packed)) PspLibStubEntry;
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Execution seems to involve looking for the .lib.ent section, reading flags and the pointer to the PspResidentData. This chunk of data has 2 magic longs (unknown what their purpose or meaning is -- they seem to work fine for nem..), the program start address, and the address of the module info data (see PspModuleInfo struct).
That's all i've got so far; I'm curious what happens if someone with a 1.0 psp makes those 2 magic longs 0 in the PspResidentData... |
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mrbrown
Joined: 17 Jan 2004
Posts: 1536
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| Posted: Fri May 06, 2005 10:15 pm Post subject: |
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Since PRX looks like a bastardized IRX (whose format is well known), the first 4 bytes of what you posted for PspModuleInfo appear to be the module version (second 2 bytes) and possibly flags. However it could also be a placeholder to link the PspModuleInfo structure into a linked list of modules, once the module is loaded.
_________________
"He was warned..." |
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nem
Joined: 13 Jan 2005
Posts: 73
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| Posted: Sat May 07, 2005 11:20 am Post subject: |
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For your interest, notes for PSP ELF format and program loader. Some need confirmation.
- ELF Type: EXEC(0x0002) NB:PRX have 0xffa0,0xff81, etc.
- ELF Flags: seems not to be used
- any section name, any section deploying is allowed, except .rodata.sceModuleInfo for module information
- .rodata.sceModuleInfo is mandantory to execute
- program loading header can be one or more
- physical address of first program loading header is file offset of module information
- can be absolute or relocatable but loading virtual address must be within 0x08900000..0x09ffffff, user memory area
- relocation info are simply omitted when loading
- module information have flags, module name, gp, export table address region(ent) and import table(stub) address region
- export/import is done by ascii string stub group name and 32bit id for each symbol
- 32bit id is independent from actual ascii symbol name as far as loader concerned
- import stub text contains jr ra, nop
- loader rewrites nop to syscall
- user program is executed in cpu's user mode |
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Warren
Joined: 24 Jan 2004
Posts: 173
Location: San Diego, CA
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| Posted: Sat May 07, 2005 11:49 am Post subject: |
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32bit symbol ID is actually the first 4 bytes of SHA1 of the symbol name.
Someone on IRC figured this out the otehr day and there is code to calculate it on the ftp server. |
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vvuk
Joined: 25 Apr 2005
Posts: 13
Location: Foster City, CA
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| Posted: Sat May 07, 2005 11:57 am Post subject: |
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| Warren wrote: | 32bit symbol ID is actually the first 4 bytes of SHA1 of the symbol name.
Someone on IRC figured this out the otehr day and there is code to calculate it on the ftp server. |
Right, what nem is saying (and as demonstrated by his code) -- the relocation is done only by the NID, the name is irrelevant. It can even be null. |
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Warren
Joined: 24 Jan 2004
Posts: 173
Location: San Diego, CA
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| Posted: Sat May 07, 2005 12:03 pm Post subject: |
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| Ahh ok, gotcha. |
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