diff options
| -rw-r--r-- | Lib/compiler/pyassem.py | 31 | ||||
| -rw-r--r-- | Misc/ACKS | 1 | ||||
| -rw-r--r-- | Python/compile.c | 64 | ||||
| -rw-r--r-- | Tools/compiler/compiler/pyassem.py | 31 |
4 files changed, 83 insertions, 44 deletions
diff --git a/Lib/compiler/pyassem.py b/Lib/compiler/pyassem.py index e8810ae..0684623 100644 --- a/Lib/compiler/pyassem.py +++ b/Lib/compiler/pyassem.py @@ -613,16 +613,16 @@ def twobyte(val): class LineAddrTable: """lnotab - This class builds the lnotab, which is undocumented but described - by com_set_lineno in compile.c. Here's an attempt at explanation: + This class builds the lnotab, which is documented in compile.c. + Here's a brief recap: For each SET_LINENO instruction after the first one, two bytes are added to lnotab. (In some cases, multiple two-byte entries are added.) The first byte is the distance in bytes between the instruction for the last SET_LINENO and the current SET_LINENO. The second byte is offset in line numbers. If either offset is - greater than 255, multiple two-byte entries are added -- one entry - for each factor of 255. + greater than 255, multiple two-byte entries are added -- see + compile.c for the delicate details. """ def __init__(self): @@ -657,19 +657,16 @@ class LineAddrTable: # compiler because it only generates a SET_LINENO instruction # for the assignment. if line > 0: - while addr > 0 or line > 0: - # write the values in 1-byte chunks that sum - # to desired value - trunc_addr = addr - trunc_line = line - if trunc_addr > 255: - trunc_addr = 255 - if trunc_line > 255: - trunc_line = 255 - self.lnotab.append(trunc_addr) - self.lnotab.append(trunc_line) - addr = addr - trunc_addr - line = line - trunc_line + push = self.lnotab.append + while addr > 255: + push(255); push(0) + addr -= 255 + while line > 255: + push(addr); push(255) + line -= 255 + addr = 0 + if addr > 0 or line > 0: + push(addr); push(line) self.lastline = lineno self.lastoff = self.codeOffset @@ -319,6 +319,7 @@ Michael P. Reilly Bernhard Reiter Steven Reiz Jan Pieter Riegel +Armin Rigo Nicholas Riley Jean-Claude Rimbault Andy Robinson diff --git a/Python/compile.c b/Python/compile.c index ec3de26..b9ba0fc 100644 --- a/Python/compile.c +++ b/Python/compile.c @@ -336,6 +336,50 @@ PyCode_New(int argcount, int nlocals, int stacksize, int flags, c_argcount, c_globals, and c_flags. */ +/* All about c_lnotab. + +c_lnotab is an array of unsigned bytes disguised as a Python string. In -O +mode, SET_LINENO opcodes aren't generated, and bytecode offsets are mapped +to source code line #s (when needed for tracebacks) via c_lnotab instead. +The array is conceptually a list of + (bytecode offset increment, line number increment) +pairs. The details are important and delicate, best illustrated by example: + + byte code offset source code line number + 0 1 + 6 2 + 50 7 + 350 307 + 361 308 + +The first trick is that these numbers aren't stored, only the increments +from one row to the next (this doesn't really work, but it's a start): + + 0, 1, 6, 1, 44, 5, 300, 300, 11, 1 + +The second trick is that an unsigned byte can't hold negative values, or +values larger than 255, so (a) there's a deep assumption that byte code +offsets and their corresponding line #s both increase monotonically, and (b) +if at least one column jumps by more than 255 from one row to the next, more +than one pair is written to the table. In case #b, there's no way to know +from looking at the table later how many were written. That's the delicate +part. A user of c_lnotab desiring to find the source line number +corresponding to a bytecode address A should do something like this + + lineno = addr = 0 + for addr_incr, line_incr in c_lnotab: + addr += addr_incr + if addr > A: + return lineno + lineno += line_incr + +In order for this to work, when the addr field increments by more than 255, +the line # increment in each pair generated must be 0 until the remaining addr +increment is < 256. So, in the example above, com_set_lineno should not (as +was actually done until 2.2) expand 300, 300 to 255, 255, 45, 45, but to +255, 0, 45, 255, 0, 45. +*/ + struct compiling { PyObject *c_code; /* string */ PyObject *c_consts; /* list of objects */ @@ -692,17 +736,17 @@ com_set_lineno(struct compiling *c, int lineno) else { int incr_addr = c->c_nexti - c->c_last_addr; int incr_line = lineno - c->c_last_line; - while (incr_addr > 0 || incr_line > 0) { - int trunc_addr = incr_addr; - int trunc_line = incr_line; - if (trunc_addr > 255) - trunc_addr = 255; - if (trunc_line > 255) - trunc_line = 255; - com_add_lnotab(c, trunc_addr, trunc_line); - incr_addr -= trunc_addr; - incr_line -= trunc_line; + while (incr_addr > 255) { + com_add_lnotab(c, 255, 0); + incr_addr -= 255; + } + while (incr_line > 255) { + com_add_lnotab(c, incr_addr, 255); + incr_line -=255; + incr_addr = 0; } + if (incr_addr > 0 || incr_line > 0) + com_add_lnotab(c, incr_addr, incr_line); c->c_last_addr = c->c_nexti; c->c_last_line = lineno; } diff --git a/Tools/compiler/compiler/pyassem.py b/Tools/compiler/compiler/pyassem.py index e8810ae..0684623 100644 --- a/Tools/compiler/compiler/pyassem.py +++ b/Tools/compiler/compiler/pyassem.py @@ -613,16 +613,16 @@ def twobyte(val): class LineAddrTable: """lnotab - This class builds the lnotab, which is undocumented but described - by com_set_lineno in compile.c. Here's an attempt at explanation: + This class builds the lnotab, which is documented in compile.c. + Here's a brief recap: For each SET_LINENO instruction after the first one, two bytes are added to lnotab. (In some cases, multiple two-byte entries are added.) The first byte is the distance in bytes between the instruction for the last SET_LINENO and the current SET_LINENO. The second byte is offset in line numbers. If either offset is - greater than 255, multiple two-byte entries are added -- one entry - for each factor of 255. + greater than 255, multiple two-byte entries are added -- see + compile.c for the delicate details. """ def __init__(self): @@ -657,19 +657,16 @@ class LineAddrTable: # compiler because it only generates a SET_LINENO instruction # for the assignment. if line > 0: - while addr > 0 or line > 0: - # write the values in 1-byte chunks that sum - # to desired value - trunc_addr = addr - trunc_line = line - if trunc_addr > 255: - trunc_addr = 255 - if trunc_line > 255: - trunc_line = 255 - self.lnotab.append(trunc_addr) - self.lnotab.append(trunc_line) - addr = addr - trunc_addr - line = line - trunc_line + push = self.lnotab.append + while addr > 255: + push(255); push(0) + addr -= 255 + while line > 255: + push(addr); push(255) + line -= 255 + addr = 0 + if addr > 0 or line > 0: + push(addr); push(line) self.lastline = lineno self.lastoff = self.codeOffset |